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179 lines
2.9 KiB
Plaintext
179 lines
2.9 KiB
Plaintext
<REFENTRY ID="SQL-EXPLAIN">
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<REFMETA>
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<REFENTRYTITLE>
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EXPLAIN
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</REFENTRYTITLE>
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<REFMISCINFO>SQL - Language Statements</REFMISCINFO>
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</REFMETA>
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<REFNAMEDIV>
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<REFNAME>
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EXPLAIN
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</REFNAME>
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<REFPURPOSE>
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Shows statement execution details
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</REFPURPOSE>
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<REFSYNOPSISDIV>
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<REFSYNOPSISDIVINFO>
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<DATE>1998-09-01</DATE>
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</REFSYNOPSISDIVINFO>
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<SYNOPSIS>
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EXPLAIN [ VERBOSE ] <REPLACEABLE CLASS="PARAMETER">query</REPLACEABLE>
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</SYNOPSIS>
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<REFSECT2 ID="R2-SQL-EXPLAIN-1">
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<REFSECT2INFO>
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<DATE>1998-09-01</DATE>
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</REFSECT2INFO>
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<TITLE>
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Inputs
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</TITLE>
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<PARA>
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<VARIABLELIST>
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<VARLISTENTRY>
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<TERM>
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VERBOSE
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</TERM>
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<LISTITEM>
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<PARA>
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Flag to show detailed query plan.
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<VARLISTENTRY>
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<TERM>
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<REPLACEABLE CLASS="PARAMETER">query</REPLACEABLE>
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</TERM>
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<LISTITEM>
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<PARA>
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Any <REPLACEABLE CLASS="PARAMETER">query</REPLACEABLE>.
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</VARIABLELIST>
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</REFSECT2>
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<REFSECT2 ID="R2-SQL-EXPLAIN-2">
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<REFSECT2INFO>
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<DATE>1998-04-15</DATE>
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</REFSECT2INFO>
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<TITLE>
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Outputs
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</TITLE>
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<PARA>
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<VARIABLELIST>
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<VARLISTENTRY>
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<TERM>
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NOTICE: QUERY PLAN:
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<replaceable>plan</replaceable>
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</TERM>
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<LISTITEM>
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<PARA>
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Explicit query plan from the <productname>Postgres</productname> backend.
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<VARIABLELIST>
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<VARLISTENTRY>
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<TERM>
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<replaceable>status</replaceable>
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</TERM>
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<LISTITEM>
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<PARA>
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<VARLISTENTRY>
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<TERM>
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EXPLAIN
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</TERM>
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<LISTITEM>
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<PARA>
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Flag sent after query plan is shown.
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</VARIABLELIST>
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</VARIABLELIST>
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</REFSECT2>
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</REFSYNOPSISDIV>
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<REFSECT1 ID="R1-SQL-EXPLAIN-1">
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<REFSECT1INFO>
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<DATE>1998-04-15</DATE>
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</REFSECT1INFO>
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<TITLE>
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Description
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</TITLE>
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<PARA>
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This command outputs details about the supplied query.
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The default output is the computed query cost.
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VERBOSE displays the full query plan and cost.
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<REFSECT2 ID="R2-SQL-EXPLAIN-3">
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<REFSECT2INFO>
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<DATE>1998-04-15</DATE>
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</REFSECT2INFO>
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<TITLE>
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Notes
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</TITLE>
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<PARA>
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There is only sparse documentation on the optimizer's use of cost
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information in <productname>Postgres</productname>.
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General information on cost estimation for query optimization
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can be found in database textbooks.
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Refer to the <citetitle>Programmer's Guide</citetitle>
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in the chapters on indexes and the genetic query optimizer for
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more information.
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</REFSECT2>
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<REFSECT1 ID="R1-SQL-EXPLAIN-2">
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<TITLE>
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Usage
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</TITLE>
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<PARA>
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To show a query plan for a simple query:
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<ProgramListing>
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postgres=> explain select * from foo;
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NOTICE: QUERY PLAN:
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Seq Scan on foo (cost=0.00 size=0 width=4)
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EXPLAIN
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</ProgramListing>
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</REFSECT1>
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<REFSECT1 ID="R1-SQL-EXPLAIN-3">
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<TITLE>
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Compatibility
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</TITLE>
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<PARA>
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</PARA>
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<REFSECT2 ID="R2-SQL-EXPLAIN-4">
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<REFSECT2INFO>
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<DATE>1998-09-01</DATE>
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</REFSECT2INFO>
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<TITLE>
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SQL92
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</TITLE>
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<PARA>
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There is no EXPLAIN statement defined in SQL92.
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</REFENTRY>
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<!--
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<REPLACEABLE CLASS="PARAMETER">
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</REPLACEABLE>
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<ReturnValue></ReturnValue>
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<PARA>
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</PARA>
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<VARIABLELIST>
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<VARLISTENTRY>
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<TERM>•
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</TERM>
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<LISTITEM>
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<PARA>
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</PARA>
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</LISTITEM>
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</VARLISTENTRY>
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</VARIABLELIST>
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<PARA>
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</PARA>
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-->
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