2018-02-06 19:52:27 +01:00
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<!-- doc/src/sgml/btree.sgml -->
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<chapter id="btree">
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<title>B-Tree Indexes</title>
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<indexterm>
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<primary>index</primary>
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<secondary>B-Tree</secondary>
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</indexterm>
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<sect1 id="btree-intro">
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<title>Introduction</title>
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<para>
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<productname>PostgreSQL</productname> includes an implementation of the
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2019-01-08 01:51:17 +01:00
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standard <acronym>btree</acronym> (multi-way balanced tree) index data
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2018-02-06 19:52:27 +01:00
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structure. Any data type that can be sorted into a well-defined linear
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order can be indexed by a btree index. The only limitation is that an
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index entry cannot exceed approximately one-third of a page (after TOAST
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compression, if applicable).
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</para>
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<para>
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Because each btree operator class imposes a sort order on its data type,
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btree operator classes (or, really, operator families) have come to be
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used as <productname>PostgreSQL</productname>'s general representation
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and understanding of sorting semantics. Therefore, they've acquired
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some features that go beyond what would be needed just to support btree
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indexes, and parts of the system that are quite distant from the
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btree AM make use of them.
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</para>
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</sect1>
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<sect1 id="btree-behavior">
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<title>Behavior of B-Tree Operator Classes</title>
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<para>
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As shown in <xref linkend="xindex-btree-strat-table"/>, a btree operator
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class must provide five comparison operators,
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<literal><</literal>,
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<literal><=</literal>,
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<literal>=</literal>,
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<literal>>=</literal> and
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<literal>></literal>.
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One might expect that <literal><></literal> should also be part of
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the operator class, but it is not, because it would almost never be
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useful to use a <literal><></literal> WHERE clause in an index
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search. (For some purposes, the planner treats <literal><></literal>
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as associated with a btree operator class; but it finds that operator via
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the <literal>=</literal> operator's negator link, rather than
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from <structname>pg_amop</structname>.)
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</para>
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<para>
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When several data types share near-identical sorting semantics, their
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operator classes can be grouped into an operator family. Doing so is
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advantageous because it allows the planner to make deductions about
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cross-type comparisons. Each operator class within the family should
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contain the single-type operators (and associated support functions)
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for its input data type, while cross-type comparison operators and
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support functions are <quote>loose</quote> in the family. It is
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recommendable that a complete set of cross-type operators be included
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in the family, thus ensuring that the planner can represent any
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comparison conditions that it deduces from transitivity.
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</para>
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<para>
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There are some basic assumptions that a btree operator family must
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satisfy:
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</para>
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<itemizedlist>
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<listitem>
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<para>
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An <literal>=</literal> operator must be an equivalence relation; that
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is, for all non-null values <replaceable>A</replaceable>,
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<replaceable>B</replaceable>, <replaceable>C</replaceable> of the
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data type:
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<itemizedlist>
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<listitem>
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<para>
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<replaceable>A</replaceable> <literal>=</literal>
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<replaceable>A</replaceable> is true
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(<firstterm>reflexive law</firstterm>)
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</para>
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</listitem>
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<listitem>
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<para>
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if <replaceable>A</replaceable> <literal>=</literal>
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<replaceable>B</replaceable>,
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then <replaceable>B</replaceable> <literal>=</literal>
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<replaceable>A</replaceable>
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(<firstterm>symmetric law</firstterm>)
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</para>
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</listitem>
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<listitem>
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<para>
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if <replaceable>A</replaceable> <literal>=</literal>
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<replaceable>B</replaceable> and <replaceable>B</replaceable>
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<literal>=</literal> <replaceable>C</replaceable>,
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then <replaceable>A</replaceable> <literal>=</literal>
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<replaceable>C</replaceable>
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(<firstterm>transitive law</firstterm>)
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</para>
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</listitem>
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</itemizedlist>
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</para>
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</listitem>
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<listitem>
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<para>
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A <literal><</literal> operator must be a strong ordering relation;
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that is, for all non-null values <replaceable>A</replaceable>,
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<replaceable>B</replaceable>, <replaceable>C</replaceable>:
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<itemizedlist>
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<listitem>
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<para>
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<replaceable>A</replaceable> <literal><</literal>
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<replaceable>A</replaceable> is false
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(<firstterm>irreflexive law</firstterm>)
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</para>
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</listitem>
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<listitem>
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<para>
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if <replaceable>A</replaceable> <literal><</literal>
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<replaceable>B</replaceable>
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and <replaceable>B</replaceable> <literal><</literal>
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<replaceable>C</replaceable>,
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then <replaceable>A</replaceable> <literal><</literal>
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<replaceable>C</replaceable>
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(<firstterm>transitive law</firstterm>)
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</para>
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</listitem>
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</itemizedlist>
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</para>
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</listitem>
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<listitem>
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<para>
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Furthermore, the ordering is total; that is, for all non-null
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values <replaceable>A</replaceable>, <replaceable>B</replaceable>:
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<itemizedlist>
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<listitem>
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<para>
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exactly one of <replaceable>A</replaceable> <literal><</literal>
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<replaceable>B</replaceable>, <replaceable>A</replaceable>
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<literal>=</literal> <replaceable>B</replaceable>, and
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<replaceable>B</replaceable> <literal><</literal>
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<replaceable>A</replaceable> is true
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(<firstterm>trichotomy law</firstterm>)
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</para>
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</listitem>
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</itemizedlist>
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(The trichotomy law justifies the definition of the comparison support
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function, of course.)
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</para>
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</listitem>
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</itemizedlist>
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<para>
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The other three operators are defined in terms of <literal>=</literal>
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and <literal><</literal> in the obvious way, and must act consistently
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with them.
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</para>
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<para>
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For an operator family supporting multiple data types, the above laws must
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hold when <replaceable>A</replaceable>, <replaceable>B</replaceable>,
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<replaceable>C</replaceable> are taken from any data types in the family.
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The transitive laws are the trickiest to ensure, as in cross-type
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situations they represent statements that the behaviors of two or three
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different operators are consistent.
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As an example, it would not work to put <type>float8</type>
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and <type>numeric</type> into the same operator family, at least not with
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the current semantics that <type>numeric</type> values are converted
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to <type>float8</type> for comparison to a <type>float8</type>. Because
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of the limited accuracy of <type>float8</type>, this means there are
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distinct <type>numeric</type> values that will compare equal to the
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same <type>float8</type> value, and thus the transitive law would fail.
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</para>
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<para>
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Another requirement for a multiple-data-type family is that any implicit
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or binary-coercion casts that are defined between data types included in
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the operator family must not change the associated sort ordering.
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</para>
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<para>
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It should be fairly clear why a btree index requires these laws to hold
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within a single data type: without them there is no ordering to arrange
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the keys with. Also, index searches using a comparison key of a
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different data type require comparisons to behave sanely across two
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data types. The extensions to three or more data types within a family
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are not strictly required by the btree index mechanism itself, but the
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planner relies on them for optimization purposes.
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</para>
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</sect1>
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<sect1 id="btree-support-funcs">
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<title>B-Tree Support Functions</title>
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<para>
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As shown in <xref linkend="xindex-btree-support-table"/>, btree defines
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2020-02-26 20:28:25 +01:00
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one required and three optional support functions. The four
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2020-02-12 23:08:34 +01:00
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user-defined methods are:
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2018-02-06 19:52:27 +01:00
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</para>
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2020-02-12 23:08:34 +01:00
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<variablelist>
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<varlistentry>
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<term><function>order</function></term>
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Support all SQL:2011 options for window frame clauses.
This patch adds the ability to use "RANGE offset PRECEDING/FOLLOWING"
frame boundaries in window functions. We'd punted on that back in the
original patch to add window functions, because it was not clear how to
do it in a reasonably data-type-extensible fashion. That problem is
resolved here by adding the ability for btree operator classes to provide
an "in_range" support function that defines how to add or subtract the
RANGE offset value. Factoring it this way also allows the operator class
to avoid overflow problems near the ends of the datatype's range, if it
wishes to expend effort on that. (In the committed patch, the integer
opclasses handle that issue, but it did not seem worth the trouble to
avoid overflow failures for datetime types.)
The patch includes in_range support for the integer_ops opfamily
(int2/int4/int8) as well as the standard datetime types. Support for
other numeric types has been requested, but that seems like suitable
material for a follow-on patch.
In addition, the patch adds GROUPS mode which counts the offset in
ORDER-BY peer groups rather than rows, and it adds the frame_exclusion
options specified by SQL:2011. As far as I can see, we are now fully
up to spec on window framing options.
Existing behaviors remain unchanged, except that I changed the errcode
for a couple of existing error reports to meet the SQL spec's expectation
that negative "offset" values should be reported as SQLSTATE 22013.
Internally and in relevant parts of the documentation, we now consistently
use the terminology "offset PRECEDING/FOLLOWING" rather than "value
PRECEDING/FOLLOWING", since the term "value" is confusingly vague.
Oliver Ford, reviewed and whacked around some by me
Discussion: https://postgr.es/m/CAGMVOdu9sivPAxbNN0X+q19Sfv9edEPv=HibOJhB14TJv_RCQg@mail.gmail.com
2018-02-07 06:06:50 +01:00
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<listitem>
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<para>
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2020-02-12 23:08:34 +01:00
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For each combination of data types that a btree operator family
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provides comparison operators for, it must provide a comparison
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support function, registered in
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<structname>pg_amproc</structname> with support function number 1
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and
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<structfield>amproclefttype</structfield>/<structfield>amprocrighttype</structfield>
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equal to the left and right data types for the comparison (i.e.,
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the same data types that the matching operators are registered
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with in <structname>pg_amop</structname>). The comparison
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function must take two non-null values
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<replaceable>A</replaceable> and <replaceable>B</replaceable> and
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return an <type>int32</type> value that is
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<literal><</literal> <literal>0</literal>,
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<literal>0</literal>, or <literal>></literal>
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<literal>0</literal> when <replaceable>A</replaceable>
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<literal><</literal> <replaceable>B</replaceable>,
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<replaceable>A</replaceable> <literal>=</literal>
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<replaceable>B</replaceable>, or <replaceable>A</replaceable>
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<literal>></literal> <replaceable>B</replaceable>,
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respectively. A null result is disallowed: all values of the
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data type must be comparable. See
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<filename>src/backend/access/nbtree/nbtcompare.c</filename> for
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examples.
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Support all SQL:2011 options for window frame clauses.
This patch adds the ability to use "RANGE offset PRECEDING/FOLLOWING"
frame boundaries in window functions. We'd punted on that back in the
original patch to add window functions, because it was not clear how to
do it in a reasonably data-type-extensible fashion. That problem is
resolved here by adding the ability for btree operator classes to provide
an "in_range" support function that defines how to add or subtract the
RANGE offset value. Factoring it this way also allows the operator class
to avoid overflow problems near the ends of the datatype's range, if it
wishes to expend effort on that. (In the committed patch, the integer
opclasses handle that issue, but it did not seem worth the trouble to
avoid overflow failures for datetime types.)
The patch includes in_range support for the integer_ops opfamily
(int2/int4/int8) as well as the standard datetime types. Support for
other numeric types has been requested, but that seems like suitable
material for a follow-on patch.
In addition, the patch adds GROUPS mode which counts the offset in
ORDER-BY peer groups rather than rows, and it adds the frame_exclusion
options specified by SQL:2011. As far as I can see, we are now fully
up to spec on window framing options.
Existing behaviors remain unchanged, except that I changed the errcode
for a couple of existing error reports to meet the SQL spec's expectation
that negative "offset" values should be reported as SQLSTATE 22013.
Internally and in relevant parts of the documentation, we now consistently
use the terminology "offset PRECEDING/FOLLOWING" rather than "value
PRECEDING/FOLLOWING", since the term "value" is confusingly vague.
Oliver Ford, reviewed and whacked around some by me
Discussion: https://postgr.es/m/CAGMVOdu9sivPAxbNN0X+q19Sfv9edEPv=HibOJhB14TJv_RCQg@mail.gmail.com
2018-02-07 06:06:50 +01:00
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</para>
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2020-02-12 23:08:34 +01:00
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Support all SQL:2011 options for window frame clauses.
This patch adds the ability to use "RANGE offset PRECEDING/FOLLOWING"
frame boundaries in window functions. We'd punted on that back in the
original patch to add window functions, because it was not clear how to
do it in a reasonably data-type-extensible fashion. That problem is
resolved here by adding the ability for btree operator classes to provide
an "in_range" support function that defines how to add or subtract the
RANGE offset value. Factoring it this way also allows the operator class
to avoid overflow problems near the ends of the datatype's range, if it
wishes to expend effort on that. (In the committed patch, the integer
opclasses handle that issue, but it did not seem worth the trouble to
avoid overflow failures for datetime types.)
The patch includes in_range support for the integer_ops opfamily
(int2/int4/int8) as well as the standard datetime types. Support for
other numeric types has been requested, but that seems like suitable
material for a follow-on patch.
In addition, the patch adds GROUPS mode which counts the offset in
ORDER-BY peer groups rather than rows, and it adds the frame_exclusion
options specified by SQL:2011. As far as I can see, we are now fully
up to spec on window framing options.
Existing behaviors remain unchanged, except that I changed the errcode
for a couple of existing error reports to meet the SQL spec's expectation
that negative "offset" values should be reported as SQLSTATE 22013.
Internally and in relevant parts of the documentation, we now consistently
use the terminology "offset PRECEDING/FOLLOWING" rather than "value
PRECEDING/FOLLOWING", since the term "value" is confusingly vague.
Oliver Ford, reviewed and whacked around some by me
Discussion: https://postgr.es/m/CAGMVOdu9sivPAxbNN0X+q19Sfv9edEPv=HibOJhB14TJv_RCQg@mail.gmail.com
2018-02-07 06:06:50 +01:00
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<para>
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2020-02-12 23:08:34 +01:00
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If the compared values are of a collatable data type, the
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appropriate collation OID will be passed to the comparison
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support function, using the standard
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<function>PG_GET_COLLATION()</function> mechanism.
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Support all SQL:2011 options for window frame clauses.
This patch adds the ability to use "RANGE offset PRECEDING/FOLLOWING"
frame boundaries in window functions. We'd punted on that back in the
original patch to add window functions, because it was not clear how to
do it in a reasonably data-type-extensible fashion. That problem is
resolved here by adding the ability for btree operator classes to provide
an "in_range" support function that defines how to add or subtract the
RANGE offset value. Factoring it this way also allows the operator class
to avoid overflow problems near the ends of the datatype's range, if it
wishes to expend effort on that. (In the committed patch, the integer
opclasses handle that issue, but it did not seem worth the trouble to
avoid overflow failures for datetime types.)
The patch includes in_range support for the integer_ops opfamily
(int2/int4/int8) as well as the standard datetime types. Support for
other numeric types has been requested, but that seems like suitable
material for a follow-on patch.
In addition, the patch adds GROUPS mode which counts the offset in
ORDER-BY peer groups rather than rows, and it adds the frame_exclusion
options specified by SQL:2011. As far as I can see, we are now fully
up to spec on window framing options.
Existing behaviors remain unchanged, except that I changed the errcode
for a couple of existing error reports to meet the SQL spec's expectation
that negative "offset" values should be reported as SQLSTATE 22013.
Internally and in relevant parts of the documentation, we now consistently
use the terminology "offset PRECEDING/FOLLOWING" rather than "value
PRECEDING/FOLLOWING", since the term "value" is confusingly vague.
Oliver Ford, reviewed and whacked around some by me
Discussion: https://postgr.es/m/CAGMVOdu9sivPAxbNN0X+q19Sfv9edEPv=HibOJhB14TJv_RCQg@mail.gmail.com
2018-02-07 06:06:50 +01:00
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</para>
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</listitem>
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2020-02-12 23:08:34 +01:00
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</varlistentry>
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<varlistentry>
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<term><function>sortsupport</function></term>
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Support all SQL:2011 options for window frame clauses.
This patch adds the ability to use "RANGE offset PRECEDING/FOLLOWING"
frame boundaries in window functions. We'd punted on that back in the
original patch to add window functions, because it was not clear how to
do it in a reasonably data-type-extensible fashion. That problem is
resolved here by adding the ability for btree operator classes to provide
an "in_range" support function that defines how to add or subtract the
RANGE offset value. Factoring it this way also allows the operator class
to avoid overflow problems near the ends of the datatype's range, if it
wishes to expend effort on that. (In the committed patch, the integer
opclasses handle that issue, but it did not seem worth the trouble to
avoid overflow failures for datetime types.)
The patch includes in_range support for the integer_ops opfamily
(int2/int4/int8) as well as the standard datetime types. Support for
other numeric types has been requested, but that seems like suitable
material for a follow-on patch.
In addition, the patch adds GROUPS mode which counts the offset in
ORDER-BY peer groups rather than rows, and it adds the frame_exclusion
options specified by SQL:2011. As far as I can see, we are now fully
up to spec on window framing options.
Existing behaviors remain unchanged, except that I changed the errcode
for a couple of existing error reports to meet the SQL spec's expectation
that negative "offset" values should be reported as SQLSTATE 22013.
Internally and in relevant parts of the documentation, we now consistently
use the terminology "offset PRECEDING/FOLLOWING" rather than "value
PRECEDING/FOLLOWING", since the term "value" is confusingly vague.
Oliver Ford, reviewed and whacked around some by me
Discussion: https://postgr.es/m/CAGMVOdu9sivPAxbNN0X+q19Sfv9edEPv=HibOJhB14TJv_RCQg@mail.gmail.com
2018-02-07 06:06:50 +01:00
|
|
|
<listitem>
|
|
|
|
<para>
|
2020-02-12 23:08:34 +01:00
|
|
|
Optionally, a btree operator family may provide <firstterm>sort
|
|
|
|
support</firstterm> function(s), registered under support
|
|
|
|
function number 2. These functions allow implementing
|
|
|
|
comparisons for sorting purposes in a more efficient way than
|
|
|
|
naively calling the comparison support function. The APIs
|
|
|
|
involved in this are defined in
|
|
|
|
<filename>src/include/utils/sortsupport.h</filename>.
|
Support all SQL:2011 options for window frame clauses.
This patch adds the ability to use "RANGE offset PRECEDING/FOLLOWING"
frame boundaries in window functions. We'd punted on that back in the
original patch to add window functions, because it was not clear how to
do it in a reasonably data-type-extensible fashion. That problem is
resolved here by adding the ability for btree operator classes to provide
an "in_range" support function that defines how to add or subtract the
RANGE offset value. Factoring it this way also allows the operator class
to avoid overflow problems near the ends of the datatype's range, if it
wishes to expend effort on that. (In the committed patch, the integer
opclasses handle that issue, but it did not seem worth the trouble to
avoid overflow failures for datetime types.)
The patch includes in_range support for the integer_ops opfamily
(int2/int4/int8) as well as the standard datetime types. Support for
other numeric types has been requested, but that seems like suitable
material for a follow-on patch.
In addition, the patch adds GROUPS mode which counts the offset in
ORDER-BY peer groups rather than rows, and it adds the frame_exclusion
options specified by SQL:2011. As far as I can see, we are now fully
up to spec on window framing options.
Existing behaviors remain unchanged, except that I changed the errcode
for a couple of existing error reports to meet the SQL spec's expectation
that negative "offset" values should be reported as SQLSTATE 22013.
Internally and in relevant parts of the documentation, we now consistently
use the terminology "offset PRECEDING/FOLLOWING" rather than "value
PRECEDING/FOLLOWING", since the term "value" is confusingly vague.
Oliver Ford, reviewed and whacked around some by me
Discussion: https://postgr.es/m/CAGMVOdu9sivPAxbNN0X+q19Sfv9edEPv=HibOJhB14TJv_RCQg@mail.gmail.com
2018-02-07 06:06:50 +01:00
|
|
|
</para>
|
|
|
|
</listitem>
|
2020-02-12 23:08:34 +01:00
|
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
|
|
<term><function>inrange</function></term>
|
Support all SQL:2011 options for window frame clauses.
This patch adds the ability to use "RANGE offset PRECEDING/FOLLOWING"
frame boundaries in window functions. We'd punted on that back in the
original patch to add window functions, because it was not clear how to
do it in a reasonably data-type-extensible fashion. That problem is
resolved here by adding the ability for btree operator classes to provide
an "in_range" support function that defines how to add or subtract the
RANGE offset value. Factoring it this way also allows the operator class
to avoid overflow problems near the ends of the datatype's range, if it
wishes to expend effort on that. (In the committed patch, the integer
opclasses handle that issue, but it did not seem worth the trouble to
avoid overflow failures for datetime types.)
The patch includes in_range support for the integer_ops opfamily
(int2/int4/int8) as well as the standard datetime types. Support for
other numeric types has been requested, but that seems like suitable
material for a follow-on patch.
In addition, the patch adds GROUPS mode which counts the offset in
ORDER-BY peer groups rather than rows, and it adds the frame_exclusion
options specified by SQL:2011. As far as I can see, we are now fully
up to spec on window framing options.
Existing behaviors remain unchanged, except that I changed the errcode
for a couple of existing error reports to meet the SQL spec's expectation
that negative "offset" values should be reported as SQLSTATE 22013.
Internally and in relevant parts of the documentation, we now consistently
use the terminology "offset PRECEDING/FOLLOWING" rather than "value
PRECEDING/FOLLOWING", since the term "value" is confusingly vague.
Oliver Ford, reviewed and whacked around some by me
Discussion: https://postgr.es/m/CAGMVOdu9sivPAxbNN0X+q19Sfv9edEPv=HibOJhB14TJv_RCQg@mail.gmail.com
2018-02-07 06:06:50 +01:00
|
|
|
<listitem>
|
2020-02-12 23:08:34 +01:00
|
|
|
<indexterm>
|
|
|
|
<primary>in_range support functions</primary>
|
|
|
|
</indexterm>
|
|
|
|
|
|
|
|
<indexterm>
|
|
|
|
<primary>support functions</primary>
|
|
|
|
<secondary>in_range</secondary>
|
|
|
|
</indexterm>
|
Support all SQL:2011 options for window frame clauses.
This patch adds the ability to use "RANGE offset PRECEDING/FOLLOWING"
frame boundaries in window functions. We'd punted on that back in the
original patch to add window functions, because it was not clear how to
do it in a reasonably data-type-extensible fashion. That problem is
resolved here by adding the ability for btree operator classes to provide
an "in_range" support function that defines how to add or subtract the
RANGE offset value. Factoring it this way also allows the operator class
to avoid overflow problems near the ends of the datatype's range, if it
wishes to expend effort on that. (In the committed patch, the integer
opclasses handle that issue, but it did not seem worth the trouble to
avoid overflow failures for datetime types.)
The patch includes in_range support for the integer_ops opfamily
(int2/int4/int8) as well as the standard datetime types. Support for
other numeric types has been requested, but that seems like suitable
material for a follow-on patch.
In addition, the patch adds GROUPS mode which counts the offset in
ORDER-BY peer groups rather than rows, and it adds the frame_exclusion
options specified by SQL:2011. As far as I can see, we are now fully
up to spec on window framing options.
Existing behaviors remain unchanged, except that I changed the errcode
for a couple of existing error reports to meet the SQL spec's expectation
that negative "offset" values should be reported as SQLSTATE 22013.
Internally and in relevant parts of the documentation, we now consistently
use the terminology "offset PRECEDING/FOLLOWING" rather than "value
PRECEDING/FOLLOWING", since the term "value" is confusingly vague.
Oliver Ford, reviewed and whacked around some by me
Discussion: https://postgr.es/m/CAGMVOdu9sivPAxbNN0X+q19Sfv9edEPv=HibOJhB14TJv_RCQg@mail.gmail.com
2018-02-07 06:06:50 +01:00
|
|
|
<para>
|
2020-02-12 23:08:34 +01:00
|
|
|
Optionally, a btree operator family may provide
|
|
|
|
<firstterm>in_range</firstterm> support function(s), registered
|
|
|
|
under support function number 3. These are not used during btree
|
|
|
|
index operations; rather, they extend the semantics of the
|
|
|
|
operator family so that it can support window clauses containing
|
|
|
|
the <literal>RANGE</literal> <replaceable>offset</replaceable>
|
|
|
|
<literal>PRECEDING</literal> and <literal>RANGE</literal>
|
|
|
|
<replaceable>offset</replaceable> <literal>FOLLOWING</literal>
|
|
|
|
frame bound types (see <xref
|
|
|
|
linkend="syntax-window-functions"/>). Fundamentally, the extra
|
|
|
|
information provided is how to add or subtract an
|
|
|
|
<replaceable>offset</replaceable> value in a way that is
|
|
|
|
compatible with the family's data ordering.
|
Support all SQL:2011 options for window frame clauses.
This patch adds the ability to use "RANGE offset PRECEDING/FOLLOWING"
frame boundaries in window functions. We'd punted on that back in the
original patch to add window functions, because it was not clear how to
do it in a reasonably data-type-extensible fashion. That problem is
resolved here by adding the ability for btree operator classes to provide
an "in_range" support function that defines how to add or subtract the
RANGE offset value. Factoring it this way also allows the operator class
to avoid overflow problems near the ends of the datatype's range, if it
wishes to expend effort on that. (In the committed patch, the integer
opclasses handle that issue, but it did not seem worth the trouble to
avoid overflow failures for datetime types.)
The patch includes in_range support for the integer_ops opfamily
(int2/int4/int8) as well as the standard datetime types. Support for
other numeric types has been requested, but that seems like suitable
material for a follow-on patch.
In addition, the patch adds GROUPS mode which counts the offset in
ORDER-BY peer groups rather than rows, and it adds the frame_exclusion
options specified by SQL:2011. As far as I can see, we are now fully
up to spec on window framing options.
Existing behaviors remain unchanged, except that I changed the errcode
for a couple of existing error reports to meet the SQL spec's expectation
that negative "offset" values should be reported as SQLSTATE 22013.
Internally and in relevant parts of the documentation, we now consistently
use the terminology "offset PRECEDING/FOLLOWING" rather than "value
PRECEDING/FOLLOWING", since the term "value" is confusingly vague.
Oliver Ford, reviewed and whacked around some by me
Discussion: https://postgr.es/m/CAGMVOdu9sivPAxbNN0X+q19Sfv9edEPv=HibOJhB14TJv_RCQg@mail.gmail.com
2018-02-07 06:06:50 +01:00
|
|
|
</para>
|
|
|
|
|
|
|
|
<para>
|
2020-02-12 23:08:34 +01:00
|
|
|
An <function>in_range</function> function must have the signature
|
|
|
|
<synopsis>
|
|
|
|
in_range(<replaceable>val</replaceable> type1, <replaceable>base</replaceable> type1, <replaceable>offset</replaceable> type2, <replaceable>sub</replaceable> bool, <replaceable>less</replaceable> bool)
|
|
|
|
returns bool
|
|
|
|
</synopsis>
|
|
|
|
<replaceable>val</replaceable> and
|
|
|
|
<replaceable>base</replaceable> must be of the same type, which
|
|
|
|
is one of the types supported by the operator family (i.e., a
|
|
|
|
type for which it provides an ordering). However,
|
|
|
|
<replaceable>offset</replaceable> could be of a different type,
|
|
|
|
which might be one otherwise unsupported by the family. An
|
|
|
|
example is that the built-in <literal>time_ops</literal> family
|
|
|
|
provides an <function>in_range</function> function that has
|
|
|
|
<replaceable>offset</replaceable> of type <type>interval</type>.
|
|
|
|
A family can provide <function>in_range</function> functions for
|
|
|
|
any of its supported types and one or more
|
|
|
|
<replaceable>offset</replaceable> types. Each
|
|
|
|
<function>in_range</function> function should be entered in
|
|
|
|
<structname>pg_amproc</structname> with
|
|
|
|
<structfield>amproclefttype</structfield> equal to
|
|
|
|
<type>type1</type> and <structfield>amprocrighttype</structfield>
|
|
|
|
equal to <type>type2</type>.
|
Support all SQL:2011 options for window frame clauses.
This patch adds the ability to use "RANGE offset PRECEDING/FOLLOWING"
frame boundaries in window functions. We'd punted on that back in the
original patch to add window functions, because it was not clear how to
do it in a reasonably data-type-extensible fashion. That problem is
resolved here by adding the ability for btree operator classes to provide
an "in_range" support function that defines how to add or subtract the
RANGE offset value. Factoring it this way also allows the operator class
to avoid overflow problems near the ends of the datatype's range, if it
wishes to expend effort on that. (In the committed patch, the integer
opclasses handle that issue, but it did not seem worth the trouble to
avoid overflow failures for datetime types.)
The patch includes in_range support for the integer_ops opfamily
(int2/int4/int8) as well as the standard datetime types. Support for
other numeric types has been requested, but that seems like suitable
material for a follow-on patch.
In addition, the patch adds GROUPS mode which counts the offset in
ORDER-BY peer groups rather than rows, and it adds the frame_exclusion
options specified by SQL:2011. As far as I can see, we are now fully
up to spec on window framing options.
Existing behaviors remain unchanged, except that I changed the errcode
for a couple of existing error reports to meet the SQL spec's expectation
that negative "offset" values should be reported as SQLSTATE 22013.
Internally and in relevant parts of the documentation, we now consistently
use the terminology "offset PRECEDING/FOLLOWING" rather than "value
PRECEDING/FOLLOWING", since the term "value" is confusingly vague.
Oliver Ford, reviewed and whacked around some by me
Discussion: https://postgr.es/m/CAGMVOdu9sivPAxbNN0X+q19Sfv9edEPv=HibOJhB14TJv_RCQg@mail.gmail.com
2018-02-07 06:06:50 +01:00
|
|
|
</para>
|
2020-02-12 23:08:34 +01:00
|
|
|
|
Support all SQL:2011 options for window frame clauses.
This patch adds the ability to use "RANGE offset PRECEDING/FOLLOWING"
frame boundaries in window functions. We'd punted on that back in the
original patch to add window functions, because it was not clear how to
do it in a reasonably data-type-extensible fashion. That problem is
resolved here by adding the ability for btree operator classes to provide
an "in_range" support function that defines how to add or subtract the
RANGE offset value. Factoring it this way also allows the operator class
to avoid overflow problems near the ends of the datatype's range, if it
wishes to expend effort on that. (In the committed patch, the integer
opclasses handle that issue, but it did not seem worth the trouble to
avoid overflow failures for datetime types.)
The patch includes in_range support for the integer_ops opfamily
(int2/int4/int8) as well as the standard datetime types. Support for
other numeric types has been requested, but that seems like suitable
material for a follow-on patch.
In addition, the patch adds GROUPS mode which counts the offset in
ORDER-BY peer groups rather than rows, and it adds the frame_exclusion
options specified by SQL:2011. As far as I can see, we are now fully
up to spec on window framing options.
Existing behaviors remain unchanged, except that I changed the errcode
for a couple of existing error reports to meet the SQL spec's expectation
that negative "offset" values should be reported as SQLSTATE 22013.
Internally and in relevant parts of the documentation, we now consistently
use the terminology "offset PRECEDING/FOLLOWING" rather than "value
PRECEDING/FOLLOWING", since the term "value" is confusingly vague.
Oliver Ford, reviewed and whacked around some by me
Discussion: https://postgr.es/m/CAGMVOdu9sivPAxbNN0X+q19Sfv9edEPv=HibOJhB14TJv_RCQg@mail.gmail.com
2018-02-07 06:06:50 +01:00
|
|
|
<para>
|
2020-02-12 23:08:34 +01:00
|
|
|
The essential semantics of an <function>in_range</function>
|
|
|
|
function depend on the two Boolean flag parameters. It should
|
|
|
|
add or subtract <replaceable>base</replaceable> and
|
|
|
|
<replaceable>offset</replaceable>, then compare
|
|
|
|
<replaceable>val</replaceable> to the result, as follows:
|
|
|
|
<itemizedlist>
|
|
|
|
<listitem>
|
|
|
|
<para>
|
|
|
|
if <literal>!</literal><replaceable>sub</replaceable> and
|
|
|
|
<literal>!</literal><replaceable>less</replaceable>, return
|
|
|
|
<replaceable>val</replaceable> <literal>>=</literal>
|
|
|
|
(<replaceable>base</replaceable> <literal>+</literal>
|
|
|
|
<replaceable>offset</replaceable>)
|
|
|
|
</para>
|
|
|
|
</listitem>
|
|
|
|
<listitem>
|
|
|
|
<para>
|
|
|
|
if <literal>!</literal><replaceable>sub</replaceable> and
|
|
|
|
<replaceable>less</replaceable>, return
|
|
|
|
<replaceable>val</replaceable> <literal><=</literal>
|
|
|
|
(<replaceable>base</replaceable> <literal>+</literal>
|
|
|
|
<replaceable>offset</replaceable>)
|
|
|
|
</para>
|
|
|
|
</listitem>
|
|
|
|
<listitem>
|
|
|
|
<para>
|
|
|
|
if <replaceable>sub</replaceable> and
|
|
|
|
<literal>!</literal><replaceable>less</replaceable>, return
|
|
|
|
<replaceable>val</replaceable> <literal>>=</literal>
|
|
|
|
(<replaceable>base</replaceable> <literal>-</literal>
|
|
|
|
<replaceable>offset</replaceable>)
|
|
|
|
</para>
|
|
|
|
</listitem>
|
|
|
|
<listitem>
|
|
|
|
<para>
|
|
|
|
if <replaceable>sub</replaceable> and
|
|
|
|
<replaceable>less</replaceable>, return
|
|
|
|
<replaceable>val</replaceable> <literal><=</literal>
|
|
|
|
(<replaceable>base</replaceable> <literal>-</literal>
|
|
|
|
<replaceable>offset</replaceable>)
|
|
|
|
</para>
|
|
|
|
</listitem>
|
|
|
|
</itemizedlist>
|
|
|
|
Before doing so, the function should check the sign of
|
|
|
|
<replaceable>offset</replaceable>: if it is less than zero, raise
|
|
|
|
error
|
|
|
|
<literal>ERRCODE_INVALID_PRECEDING_OR_FOLLOWING_SIZE</literal>
|
|
|
|
(22013) with error text like <quote>invalid preceding or
|
|
|
|
following size in window function</quote>. (This is required by
|
|
|
|
the SQL standard, although nonstandard operator families might
|
|
|
|
perhaps choose to ignore this restriction, since there seems to
|
|
|
|
be little semantic necessity for it.) This requirement is
|
|
|
|
delegated to the <function>in_range</function> function so that
|
|
|
|
the core code needn't understand what <quote>less than
|
|
|
|
zero</quote> means for a particular data type.
|
Support all SQL:2011 options for window frame clauses.
This patch adds the ability to use "RANGE offset PRECEDING/FOLLOWING"
frame boundaries in window functions. We'd punted on that back in the
original patch to add window functions, because it was not clear how to
do it in a reasonably data-type-extensible fashion. That problem is
resolved here by adding the ability for btree operator classes to provide
an "in_range" support function that defines how to add or subtract the
RANGE offset value. Factoring it this way also allows the operator class
to avoid overflow problems near the ends of the datatype's range, if it
wishes to expend effort on that. (In the committed patch, the integer
opclasses handle that issue, but it did not seem worth the trouble to
avoid overflow failures for datetime types.)
The patch includes in_range support for the integer_ops opfamily
(int2/int4/int8) as well as the standard datetime types. Support for
other numeric types has been requested, but that seems like suitable
material for a follow-on patch.
In addition, the patch adds GROUPS mode which counts the offset in
ORDER-BY peer groups rather than rows, and it adds the frame_exclusion
options specified by SQL:2011. As far as I can see, we are now fully
up to spec on window framing options.
Existing behaviors remain unchanged, except that I changed the errcode
for a couple of existing error reports to meet the SQL spec's expectation
that negative "offset" values should be reported as SQLSTATE 22013.
Internally and in relevant parts of the documentation, we now consistently
use the terminology "offset PRECEDING/FOLLOWING" rather than "value
PRECEDING/FOLLOWING", since the term "value" is confusingly vague.
Oliver Ford, reviewed and whacked around some by me
Discussion: https://postgr.es/m/CAGMVOdu9sivPAxbNN0X+q19Sfv9edEPv=HibOJhB14TJv_RCQg@mail.gmail.com
2018-02-07 06:06:50 +01:00
|
|
|
</para>
|
2020-02-12 23:08:34 +01:00
|
|
|
|
Support all SQL:2011 options for window frame clauses.
This patch adds the ability to use "RANGE offset PRECEDING/FOLLOWING"
frame boundaries in window functions. We'd punted on that back in the
original patch to add window functions, because it was not clear how to
do it in a reasonably data-type-extensible fashion. That problem is
resolved here by adding the ability for btree operator classes to provide
an "in_range" support function that defines how to add or subtract the
RANGE offset value. Factoring it this way also allows the operator class
to avoid overflow problems near the ends of the datatype's range, if it
wishes to expend effort on that. (In the committed patch, the integer
opclasses handle that issue, but it did not seem worth the trouble to
avoid overflow failures for datetime types.)
The patch includes in_range support for the integer_ops opfamily
(int2/int4/int8) as well as the standard datetime types. Support for
other numeric types has been requested, but that seems like suitable
material for a follow-on patch.
In addition, the patch adds GROUPS mode which counts the offset in
ORDER-BY peer groups rather than rows, and it adds the frame_exclusion
options specified by SQL:2011. As far as I can see, we are now fully
up to spec on window framing options.
Existing behaviors remain unchanged, except that I changed the errcode
for a couple of existing error reports to meet the SQL spec's expectation
that negative "offset" values should be reported as SQLSTATE 22013.
Internally and in relevant parts of the documentation, we now consistently
use the terminology "offset PRECEDING/FOLLOWING" rather than "value
PRECEDING/FOLLOWING", since the term "value" is confusingly vague.
Oliver Ford, reviewed and whacked around some by me
Discussion: https://postgr.es/m/CAGMVOdu9sivPAxbNN0X+q19Sfv9edEPv=HibOJhB14TJv_RCQg@mail.gmail.com
2018-02-07 06:06:50 +01:00
|
|
|
<para>
|
2020-02-12 23:08:34 +01:00
|
|
|
An additional expectation is that <function>in_range</function>
|
|
|
|
functions should, if practical, avoid throwing an error if
|
|
|
|
<replaceable>base</replaceable> <literal>+</literal>
|
|
|
|
<replaceable>offset</replaceable> or
|
|
|
|
<replaceable>base</replaceable> <literal>-</literal>
|
|
|
|
<replaceable>offset</replaceable> would overflow. The correct
|
|
|
|
comparison result can be determined even if that value would be
|
|
|
|
out of the data type's range. Note that if the data type
|
|
|
|
includes concepts such as <quote>infinity</quote> or
|
|
|
|
<quote>NaN</quote>, extra care may be needed to ensure that
|
|
|
|
<function>in_range</function>'s results agree with the normal
|
|
|
|
sort order of the operator family.
|
Support all SQL:2011 options for window frame clauses.
This patch adds the ability to use "RANGE offset PRECEDING/FOLLOWING"
frame boundaries in window functions. We'd punted on that back in the
original patch to add window functions, because it was not clear how to
do it in a reasonably data-type-extensible fashion. That problem is
resolved here by adding the ability for btree operator classes to provide
an "in_range" support function that defines how to add or subtract the
RANGE offset value. Factoring it this way also allows the operator class
to avoid overflow problems near the ends of the datatype's range, if it
wishes to expend effort on that. (In the committed patch, the integer
opclasses handle that issue, but it did not seem worth the trouble to
avoid overflow failures for datetime types.)
The patch includes in_range support for the integer_ops opfamily
(int2/int4/int8) as well as the standard datetime types. Support for
other numeric types has been requested, but that seems like suitable
material for a follow-on patch.
In addition, the patch adds GROUPS mode which counts the offset in
ORDER-BY peer groups rather than rows, and it adds the frame_exclusion
options specified by SQL:2011. As far as I can see, we are now fully
up to spec on window framing options.
Existing behaviors remain unchanged, except that I changed the errcode
for a couple of existing error reports to meet the SQL spec's expectation
that negative "offset" values should be reported as SQLSTATE 22013.
Internally and in relevant parts of the documentation, we now consistently
use the terminology "offset PRECEDING/FOLLOWING" rather than "value
PRECEDING/FOLLOWING", since the term "value" is confusingly vague.
Oliver Ford, reviewed and whacked around some by me
Discussion: https://postgr.es/m/CAGMVOdu9sivPAxbNN0X+q19Sfv9edEPv=HibOJhB14TJv_RCQg@mail.gmail.com
2018-02-07 06:06:50 +01:00
|
|
|
</para>
|
2020-02-12 23:08:34 +01:00
|
|
|
|
Support all SQL:2011 options for window frame clauses.
This patch adds the ability to use "RANGE offset PRECEDING/FOLLOWING"
frame boundaries in window functions. We'd punted on that back in the
original patch to add window functions, because it was not clear how to
do it in a reasonably data-type-extensible fashion. That problem is
resolved here by adding the ability for btree operator classes to provide
an "in_range" support function that defines how to add or subtract the
RANGE offset value. Factoring it this way also allows the operator class
to avoid overflow problems near the ends of the datatype's range, if it
wishes to expend effort on that. (In the committed patch, the integer
opclasses handle that issue, but it did not seem worth the trouble to
avoid overflow failures for datetime types.)
The patch includes in_range support for the integer_ops opfamily
(int2/int4/int8) as well as the standard datetime types. Support for
other numeric types has been requested, but that seems like suitable
material for a follow-on patch.
In addition, the patch adds GROUPS mode which counts the offset in
ORDER-BY peer groups rather than rows, and it adds the frame_exclusion
options specified by SQL:2011. As far as I can see, we are now fully
up to spec on window framing options.
Existing behaviors remain unchanged, except that I changed the errcode
for a couple of existing error reports to meet the SQL spec's expectation
that negative "offset" values should be reported as SQLSTATE 22013.
Internally and in relevant parts of the documentation, we now consistently
use the terminology "offset PRECEDING/FOLLOWING" rather than "value
PRECEDING/FOLLOWING", since the term "value" is confusingly vague.
Oliver Ford, reviewed and whacked around some by me
Discussion: https://postgr.es/m/CAGMVOdu9sivPAxbNN0X+q19Sfv9edEPv=HibOJhB14TJv_RCQg@mail.gmail.com
2018-02-07 06:06:50 +01:00
|
|
|
<para>
|
2020-02-12 23:08:34 +01:00
|
|
|
The results of the <function>in_range</function> function must be
|
|
|
|
consistent with the sort ordering imposed by the operator family.
|
|
|
|
To be precise, given any fixed values of
|
|
|
|
<replaceable>offset</replaceable> and
|
|
|
|
<replaceable>sub</replaceable>, then:
|
|
|
|
<itemizedlist>
|
|
|
|
<listitem>
|
|
|
|
<para>
|
|
|
|
If <function>in_range</function> with
|
|
|
|
<replaceable>less</replaceable> = true is true for some
|
|
|
|
<replaceable>val1</replaceable> and
|
|
|
|
<replaceable>base</replaceable>, it must be true for every
|
|
|
|
<replaceable>val2</replaceable> <literal><=</literal>
|
|
|
|
<replaceable>val1</replaceable> with the same
|
|
|
|
<replaceable>base</replaceable>.
|
|
|
|
</para>
|
|
|
|
</listitem>
|
|
|
|
<listitem>
|
|
|
|
<para>
|
|
|
|
If <function>in_range</function> with
|
|
|
|
<replaceable>less</replaceable> = true is false for some
|
|
|
|
<replaceable>val1</replaceable> and
|
|
|
|
<replaceable>base</replaceable>, it must be false for every
|
|
|
|
<replaceable>val2</replaceable> <literal>>=</literal>
|
|
|
|
<replaceable>val1</replaceable> with the same
|
|
|
|
<replaceable>base</replaceable>.
|
|
|
|
</para>
|
|
|
|
</listitem>
|
|
|
|
<listitem>
|
|
|
|
<para>
|
|
|
|
If <function>in_range</function> with
|
|
|
|
<replaceable>less</replaceable> = true is true for some
|
|
|
|
<replaceable>val</replaceable> and
|
|
|
|
<replaceable>base1</replaceable>, it must be true for every
|
|
|
|
<replaceable>base2</replaceable> <literal>>=</literal>
|
|
|
|
<replaceable>base1</replaceable> with the same
|
|
|
|
<replaceable>val</replaceable>.
|
|
|
|
</para>
|
|
|
|
</listitem>
|
|
|
|
<listitem>
|
|
|
|
<para>
|
|
|
|
If <function>in_range</function> with
|
|
|
|
<replaceable>less</replaceable> = true is false for some
|
|
|
|
<replaceable>val</replaceable> and
|
|
|
|
<replaceable>base1</replaceable>, it must be false for every
|
|
|
|
<replaceable>base2</replaceable> <literal><=</literal>
|
|
|
|
<replaceable>base1</replaceable> with the same
|
|
|
|
<replaceable>val</replaceable>.
|
|
|
|
</para>
|
|
|
|
</listitem>
|
|
|
|
</itemizedlist>
|
|
|
|
Analogous statements with inverted conditions hold when
|
|
|
|
<replaceable>less</replaceable> = false.
|
Support all SQL:2011 options for window frame clauses.
This patch adds the ability to use "RANGE offset PRECEDING/FOLLOWING"
frame boundaries in window functions. We'd punted on that back in the
original patch to add window functions, because it was not clear how to
do it in a reasonably data-type-extensible fashion. That problem is
resolved here by adding the ability for btree operator classes to provide
an "in_range" support function that defines how to add or subtract the
RANGE offset value. Factoring it this way also allows the operator class
to avoid overflow problems near the ends of the datatype's range, if it
wishes to expend effort on that. (In the committed patch, the integer
opclasses handle that issue, but it did not seem worth the trouble to
avoid overflow failures for datetime types.)
The patch includes in_range support for the integer_ops opfamily
(int2/int4/int8) as well as the standard datetime types. Support for
other numeric types has been requested, but that seems like suitable
material for a follow-on patch.
In addition, the patch adds GROUPS mode which counts the offset in
ORDER-BY peer groups rather than rows, and it adds the frame_exclusion
options specified by SQL:2011. As far as I can see, we are now fully
up to spec on window framing options.
Existing behaviors remain unchanged, except that I changed the errcode
for a couple of existing error reports to meet the SQL spec's expectation
that negative "offset" values should be reported as SQLSTATE 22013.
Internally and in relevant parts of the documentation, we now consistently
use the terminology "offset PRECEDING/FOLLOWING" rather than "value
PRECEDING/FOLLOWING", since the term "value" is confusingly vague.
Oliver Ford, reviewed and whacked around some by me
Discussion: https://postgr.es/m/CAGMVOdu9sivPAxbNN0X+q19Sfv9edEPv=HibOJhB14TJv_RCQg@mail.gmail.com
2018-02-07 06:06:50 +01:00
|
|
|
</para>
|
|
|
|
|
2020-02-12 23:08:34 +01:00
|
|
|
<para>
|
|
|
|
If the type being ordered (<type>type1</type>) is collatable, the
|
|
|
|
appropriate collation OID will be passed to the
|
|
|
|
<function>in_range</function> function, using the standard
|
|
|
|
PG_GET_COLLATION() mechanism.
|
|
|
|
</para>
|
Support all SQL:2011 options for window frame clauses.
This patch adds the ability to use "RANGE offset PRECEDING/FOLLOWING"
frame boundaries in window functions. We'd punted on that back in the
original patch to add window functions, because it was not clear how to
do it in a reasonably data-type-extensible fashion. That problem is
resolved here by adding the ability for btree operator classes to provide
an "in_range" support function that defines how to add or subtract the
RANGE offset value. Factoring it this way also allows the operator class
to avoid overflow problems near the ends of the datatype's range, if it
wishes to expend effort on that. (In the committed patch, the integer
opclasses handle that issue, but it did not seem worth the trouble to
avoid overflow failures for datetime types.)
The patch includes in_range support for the integer_ops opfamily
(int2/int4/int8) as well as the standard datetime types. Support for
other numeric types has been requested, but that seems like suitable
material for a follow-on patch.
In addition, the patch adds GROUPS mode which counts the offset in
ORDER-BY peer groups rather than rows, and it adds the frame_exclusion
options specified by SQL:2011. As far as I can see, we are now fully
up to spec on window framing options.
Existing behaviors remain unchanged, except that I changed the errcode
for a couple of existing error reports to meet the SQL spec's expectation
that negative "offset" values should be reported as SQLSTATE 22013.
Internally and in relevant parts of the documentation, we now consistently
use the terminology "offset PRECEDING/FOLLOWING" rather than "value
PRECEDING/FOLLOWING", since the term "value" is confusingly vague.
Oliver Ford, reviewed and whacked around some by me
Discussion: https://postgr.es/m/CAGMVOdu9sivPAxbNN0X+q19Sfv9edEPv=HibOJhB14TJv_RCQg@mail.gmail.com
2018-02-07 06:06:50 +01:00
|
|
|
|
2020-02-12 23:08:34 +01:00
|
|
|
<para>
|
|
|
|
<function>in_range</function> functions need not handle NULL
|
|
|
|
inputs, and typically will be marked strict.
|
|
|
|
</para>
|
|
|
|
</listitem>
|
|
|
|
</varlistentry>
|
2020-02-26 20:28:25 +01:00
|
|
|
<varlistentry>
|
|
|
|
<term><function>equalimage</function></term>
|
|
|
|
<listitem>
|
|
|
|
<para>
|
|
|
|
Optionally, a btree operator family may provide
|
|
|
|
<function>equalimage</function> (<quote>equality implies image
|
|
|
|
equality</quote>) support functions, registered under support
|
|
|
|
function number 4. These functions allow the core code to
|
|
|
|
determine when it is safe to apply the btree deduplication
|
|
|
|
optimization. Currently, <function>equalimage</function>
|
|
|
|
functions are only called when building or rebuilding an index.
|
|
|
|
</para>
|
|
|
|
<para>
|
|
|
|
An <function>equalimage</function> function must have the
|
|
|
|
signature
|
|
|
|
<synopsis>
|
|
|
|
equalimage(<replaceable>opcintype</replaceable> <type>oid</type>) returns bool
|
|
|
|
</synopsis>
|
|
|
|
The return value is static information about an operator class
|
|
|
|
and collation. Returning <literal>true</literal> indicates that
|
|
|
|
the <function>order</function> function for the operator class is
|
|
|
|
guaranteed to only return <literal>0</literal> (<quote>arguments
|
|
|
|
are equal</quote>) when its <replaceable>A</replaceable> and
|
|
|
|
<replaceable>B</replaceable> arguments are also interchangeable
|
|
|
|
without any loss of semantic information. Not registering an
|
|
|
|
<function>equalimage</function> function or returning
|
|
|
|
<literal>false</literal> indicates that this condition cannot be
|
|
|
|
assumed to hold.
|
|
|
|
</para>
|
|
|
|
<para>
|
|
|
|
The <replaceable>opcintype</replaceable> argument is the
|
|
|
|
<literal><structname>pg_type</structname>.oid</literal> of the
|
|
|
|
data type that the operator class indexes. This is a convenience
|
|
|
|
that allows reuse of the same underlying
|
|
|
|
<function>equalimage</function> function across operator classes.
|
|
|
|
If <replaceable>opcintype</replaceable> is a collatable data
|
|
|
|
type, the appropriate collation OID will be passed to the
|
|
|
|
<function>equalimage</function> function, using the standard
|
|
|
|
<function>PG_GET_COLLATION()</function> mechanism.
|
|
|
|
</para>
|
|
|
|
<para>
|
|
|
|
As far as the operator class is concerned, returning
|
|
|
|
<literal>true</literal> indicates that deduplication is safe (or
|
|
|
|
safe for the collation whose OID was passed to its
|
|
|
|
<function>equalimage</function> function). However, the core
|
|
|
|
code will only deem deduplication safe for an index when
|
|
|
|
<emphasis>every</emphasis> indexed column uses an operator class
|
|
|
|
that registers an <function>equalimage</function> function, and
|
|
|
|
each function actually returns <literal>true</literal> when
|
|
|
|
called.
|
|
|
|
</para>
|
|
|
|
<para>
|
|
|
|
Image equality is <emphasis>almost</emphasis> the same condition
|
|
|
|
as simple bitwise equality. There is one subtle difference: When
|
|
|
|
indexing a varlena data type, the on-disk representation of two
|
|
|
|
image equal datums may not be bitwise equal due to inconsistent
|
|
|
|
application of <acronym>TOAST</acronym> compression on input.
|
|
|
|
Formally, when an operator class's
|
|
|
|
<function>equalimage</function> function returns
|
|
|
|
<literal>true</literal>, it is safe to assume that the
|
|
|
|
<literal>datum_image_eq()</literal> C function will always agree
|
|
|
|
with the operator class's <function>order</function> function
|
|
|
|
(provided that the same collation OID is passed to both the
|
|
|
|
<function>equalimage</function> and <function>order</function>
|
|
|
|
functions).
|
|
|
|
</para>
|
|
|
|
<para>
|
|
|
|
The core code is fundamentally unable to deduce anything about
|
|
|
|
the <quote>equality implies image equality</quote> status of an
|
|
|
|
operator class within a multiple-data-type family based on
|
|
|
|
details from other operator classes in the same family. Also, it
|
|
|
|
is not sensible for an operator family to register a cross-type
|
|
|
|
<function>equalimage</function> function, and attempting to do so
|
|
|
|
will result in an error. This is because <quote>equality implies
|
|
|
|
image equality</quote> status does not just depend on
|
|
|
|
sorting/equality semantics, which are more or less defined at the
|
|
|
|
operator family level. In general, the semantics that one
|
|
|
|
particular data type implements must be considered separately.
|
|
|
|
</para>
|
|
|
|
<para>
|
|
|
|
The convention followed by the operator classes included with the
|
|
|
|
core <productname>PostgreSQL</productname> distribution is to
|
|
|
|
register a stock, generic <function>equalimage</function>
|
|
|
|
function. Most operator classes register
|
|
|
|
<function>btequalimage()</function>, which indicates that
|
|
|
|
deduplication is safe unconditionally. Operator classes for
|
|
|
|
collatable data types such as <type>text</type> register
|
|
|
|
<function>btvarstrequalimage()</function>, which indicates that
|
|
|
|
deduplication is safe with deterministic collations. Best
|
|
|
|
practice for third-party extensions is to register their own
|
|
|
|
custom function to retain control.
|
|
|
|
</para>
|
|
|
|
</listitem>
|
|
|
|
</varlistentry>
|
2020-02-12 23:08:34 +01:00
|
|
|
</variablelist>
|
Support all SQL:2011 options for window frame clauses.
This patch adds the ability to use "RANGE offset PRECEDING/FOLLOWING"
frame boundaries in window functions. We'd punted on that back in the
original patch to add window functions, because it was not clear how to
do it in a reasonably data-type-extensible fashion. That problem is
resolved here by adding the ability for btree operator classes to provide
an "in_range" support function that defines how to add or subtract the
RANGE offset value. Factoring it this way also allows the operator class
to avoid overflow problems near the ends of the datatype's range, if it
wishes to expend effort on that. (In the committed patch, the integer
opclasses handle that issue, but it did not seem worth the trouble to
avoid overflow failures for datetime types.)
The patch includes in_range support for the integer_ops opfamily
(int2/int4/int8) as well as the standard datetime types. Support for
other numeric types has been requested, but that seems like suitable
material for a follow-on patch.
In addition, the patch adds GROUPS mode which counts the offset in
ORDER-BY peer groups rather than rows, and it adds the frame_exclusion
options specified by SQL:2011. As far as I can see, we are now fully
up to spec on window framing options.
Existing behaviors remain unchanged, except that I changed the errcode
for a couple of existing error reports to meet the SQL spec's expectation
that negative "offset" values should be reported as SQLSTATE 22013.
Internally and in relevant parts of the documentation, we now consistently
use the terminology "offset PRECEDING/FOLLOWING" rather than "value
PRECEDING/FOLLOWING", since the term "value" is confusingly vague.
Oliver Ford, reviewed and whacked around some by me
Discussion: https://postgr.es/m/CAGMVOdu9sivPAxbNN0X+q19Sfv9edEPv=HibOJhB14TJv_RCQg@mail.gmail.com
2018-02-07 06:06:50 +01:00
|
|
|
|
2018-02-06 19:52:27 +01:00
|
|
|
</sect1>
|
|
|
|
|
|
|
|
<sect1 id="btree-implementation">
|
|
|
|
<title>Implementation</title>
|
|
|
|
|
|
|
|
<para>
|
|
|
|
An introduction to the btree index implementation can be found in
|
|
|
|
<filename>src/backend/access/nbtree/README</filename>.
|
|
|
|
</para>
|
|
|
|
|
|
|
|
</sect1>
|
|
|
|
|
|
|
|
</chapter>
|