Bruce Momjian
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doc/FAQ
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doc/FAQ
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Frequently Asked Questions (FAQ) for PostgreSQL
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Last updated: Fri Jul 29 10:05:09 EDT 2005
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Last updated: Wed Aug 10 15:29:42 EDT 2005
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Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
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4.19) Why do I get "relation with OID ##### does not exist" errors
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when accessing temporary tables in PL/PgSQL functions?
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4.20) What replication solutions are available?
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4.21) Why are my table and column names not recognized in my query?
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_________________________________________________________________
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General Questions
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The maximum table size and maximum number of columns can be quadrupled
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by increasing the default block size to 32k.
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One limitation is that indexes can not be created on columns longer
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than about 2,000 characters. Fortunately, such indexes are rarely
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needed. Uniqueness is best guaranteed using another column that is an
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MD5 hash of the long column, and full text indexing allows for
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searching of words within the column.
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4.5) How much database disk space is required to store data from a typical
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text file?
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expresssion index, it will be used:
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CREATE INDEX tabindex ON tab (lower(col));
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If the above index is created as UNIQUE, though the column can store
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upper and lowercase characters, it can not have identical values that
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differ only in case. To force a particular case to be stored in the
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column, use a CHECK constraint or a trigger.
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4.9) In a query, how do I detect if a field is NULL? How can I sort on
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whether a field is NULL or not?
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@ -776,3 +788,16 @@
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There are also commercial and hardware-based replication solutions
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available supporting a variety of replication models.
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4.20) Why are my table and column names not recognized in my query?
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The most common cause is the use of double-quotes around table or
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column names during table creation. When double-quotes are used, table
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and column names (called identifiers) are stored case-sensitive,
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meaning you must use double-quotes when referencing the names in a
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query. Some interfaces, like pgAdmin, automatically double-quote
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identifiers during table creation. So, for identifiers to be
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recognized, you must either:
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* Avoid double-quoting identifiers when creating tables
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* Use only lowercase characters in identifiers
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* Double-quote identifiers when referencing them in queries
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alink="#0000ff">
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<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1>
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<P>Last updated: Mon May 30 09:11:03 EDT 2005</P>
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<P>Last updated: Wed Aug 10 15:29:42 EDT 2005</P>
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<P>Current maintainer: Bruce Momjian (<A href=
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"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)
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<HR>
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<H2 align="center">General Questions</H2>
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<A href="#1.1">1.1</A>) What is PostgreSQL? How is it pronounced?<BR>
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<A href="#1.1">1.1</A>) What is PostgreSQL? How is it pronounced?<BR>
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<A href="#1.2">1.2</A>) What is the copyright of PostgreSQL?<BR>
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<A href="#1.3">1.3</A>) What platforms does PostgreSQL support?<BR>
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<A href="#1.4">1.4</A>) Where can I get PostgreSQL?<BR>
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does not exist" errors when accessing temporary tables in PL/PgSQL
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functions?<BR>
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<A href="#4.20">4.20</A>) What replication solutions are available?<BR>
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<A href="#4.21">4.21</A>) Why are my table and column names not
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recognized in my query?<BR>
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<HR>
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@ -124,8 +126,10 @@
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<H3><A name="1.1">1.1</A>) What is PostgreSQL? How is it pronounced?</H3>
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<P>PostgreSQL is pronounced <I>Post-Gres-Q-L</I>, also called just
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<I>Postgres</I>.</P>
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<P>PostgreSQL is pronounced <I>Post-Gres-Q-L</I>, and is also sometimes
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referred to as just <I>Postgres</I>. An audio file is available in
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<a href="http://www.postgresql.org/files/postgresql.mp3">MP3 format</a> for
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those would like to hear the pronunciation.</P>
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<P>PostgreSQL is an object-relational database system that has the
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features of traditional commercial database systems with
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@ -613,6 +617,12 @@ table?</TD><TD>unlimited</TD></TR>
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<P>The maximum table size and maximum number of columns can be
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quadrupled by increasing the default block size to 32k.</P>
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<P>One limitation is that indexes can not be created on columns
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longer than about 2,000 characters. Fortunately, such indexes are
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rarely needed. Uniqueness is best guaranteed using another column
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that is an MD5 hash of the long column, and full text indexing
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allows for searching of words within the column.</P>
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<H3><A name="4.5">4.5</A>) How much database disk space is required
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to store data from a typical text file?</H3>
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@ -740,7 +750,12 @@ table?</TD><TD>unlimited</TD></TR>
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<PRE>
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CREATE INDEX tabindex ON tab (lower(col));
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</PRE>
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<P>If the above index is created as <SMALL>UNIQUE</SMALL>, though
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the column can store upper and lowercase characters, it can not have
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identical values that differ only in case. To force a particular
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case to be stored in the column, use a <SMALL>CHECK</SMALL>
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constraint or a trigger.</P>
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<H3><A name="4.9">4.9</A>) In a query, how do I detect if a field
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is <SMALL>NULL</SMALL>? How can I sort on whether a field is <SMALL>
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NULL</SMALL> or not?</H3>
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@ -1000,5 +1015,22 @@ length</TD></TR>
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<P>There are also commercial and hardware-based replication solutions
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available supporting a variety of replication models.</P>
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<H3><A name="4.20">4.20</A>) Why are my table and column names not
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recognized in my query?</H3>
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<P>The most common cause is the use of double-quotes around table or
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column names during table creation. When double-quotes are used,
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table and column names (called identifiers) are stored <a
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href="http://www.postgresql.org/docs/8.0/static/sql-syntax.html#SQL-
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SYNTAX-IDENTIFIERS">case-sensitive</a>, meaning you must use
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double-quotes when referencing the names in a query. Some interfaces,
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like pgAdmin, automatically double-quote identifiers during table
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creation. So, for identifiers to be recognized, you must either:
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<UL>
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<LI>Avoid double-quoting identifiers when creating tables</LI>
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<LI>Use only lowercase characters in identifiers</LI>
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<LI>Double-quote identifiers when referencing them in queries</LI>
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</UL>
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</BODY>
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</HTML>
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