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Frequently Asked Questions (FAQ) for PostgreSQL Frequently Asked Questions (FAQ) for PostgreSQL
Last updated: Tue Nov 22 10:04:06 EST 2005 Last updated: Tue Nov 22 10:12:24 EST 2005
Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us) Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)

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Developer's Frequently Asked Questions (FAQ) for PostgreSQL Developer's Frequently Asked Questions (FAQ) for PostgreSQL
Last updated: Thu Oct 27 09:48:14 EDT 2005 Last updated: Tue Nov 22 10:13:04 EST 2005
Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us) Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)

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@ -10,7 +10,7 @@
alink="#0000ff"> alink="#0000ff">
<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1> <H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1>
<P>Last updated: Tue Nov 22 10:04:06 EST 2005</P> <P>Last updated: Tue Nov 22 10:12:24 EST 2005</P>
<P>Current maintainer: Bruce Momjian (<A href= <P>Current maintainer: Bruce Momjian (<A href=
"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>) "mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)
@ -124,7 +124,7 @@
<H2 align="center">General Questions</H2> <H2 align="center">General Questions</H2>
<H3><A name="1.1">1.1</A>) What is PostgreSQL? How is it pronounced?</H3> <H3 ID="1.1">1.1) What is PostgreSQL? How is it pronounced?</H3>
<P>PostgreSQL is pronounced <I>Post-Gres-Q-L</I>, and is also sometimes <P>PostgreSQL is pronounced <I>Post-Gres-Q-L</I>, and is also sometimes
referred to as just <I>Postgres</I>. An audio file is available in referred to as just <I>Postgres</I>. An audio file is available in
@ -145,7 +145,7 @@
http://www.postgresql.org/files/documentation/faqs/FAQ_DEV.html</A> http://www.postgresql.org/files/documentation/faqs/FAQ_DEV.html</A>
</P> </P>
<H3><A name="1.2">1.2</A>) Who controls PostgreSQL?<BR></H3> <H3 ID="1.2">1.2) Who controls PostgreSQL?<BR></H3>
<P>If you are looking for a PostgreSQL gatekeeper, central committee, <P>If you are looking for a PostgreSQL gatekeeper, central committee,
or controlling company, give up --- there isn't one. We do have a or controlling company, give up --- there isn't one. We do have a
@ -157,7 +157,7 @@
Developer's FAQ</A> for information on how to get involved in PostgreSQL Developer's FAQ</A> for information on how to get involved in PostgreSQL
development.)</P> development.)</P>
<H3><A name="1.3">1.3</A>) What is the copyright of <H3 ID="1.3">1.3) What is the copyright of
PostgreSQL?</H3> PostgreSQL?</H3>
<P>PostgreSQL is distributed under the classic BSD license. Basically, <P>PostgreSQL is distributed under the classic BSD license. Basically,
@ -191,7 +191,7 @@
UNIVERSITY OF CALIFORNIA HAS NO OBLIGATIONS TO PROVIDE MAINTENANCE, UNIVERSITY OF CALIFORNIA HAS NO OBLIGATIONS TO PROVIDE MAINTENANCE,
SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.</P> SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.</P>
<H3><A name="1.4">1.4</A>) What platforms does PostgreSQL support?</H3> <H3 ID="1.4">1.4) What platforms does PostgreSQL support?</H3>
<P>In general, any modern Unix-compatible platform should be able to <P>In general, any modern Unix-compatible platform should be able to
run PostgreSQL. The platforms that had received explicit testing at run PostgreSQL. The platforms that had received explicit testing at
@ -210,21 +210,21 @@
"http://hobbes.nmsu.edu/cgi-bin/h-search?sh=1&amp;button=Search&amp;key=postgreSQL&amp;stype=all&amp;sort=type&amp;dir=%2F"> "http://hobbes.nmsu.edu/cgi-bin/h-search?sh=1&amp;button=Search&amp;key=postgreSQL&amp;stype=all&amp;sort=type&amp;dir=%2F">
http://hobbes.nmsu.edu/cgi-bin/h-search?sh=1&amp;button=Search&amp;key=postgreSQL&amp;stype=all&amp;sort=type&amp;dir=%2F</a>.</p> http://hobbes.nmsu.edu/cgi-bin/h-search?sh=1&amp;button=Search&amp;key=postgreSQL&amp;stype=all&amp;sort=type&amp;dir=%2F</a>.</p>
<H3><A name="1.5">1.5</A>) Where can I get PostgreSQL?</H3> <H3 ID="1.5">1.5) Where can I get PostgreSQL?</H3>
<P>Via web browser, use <a href="http://www.postgresql.org/ftp/"> <P>Via web browser, use <a href="http://www.postgresql.org/ftp/">
http://www.postgresql.org/ftp/</a>, and via ftp, use http://www.postgresql.org/ftp/</a>, and via ftp, use
<A href="ftp://ftp.PostgreSQL.org/pub/"> <A href="ftp://ftp.PostgreSQL.org/pub/">
ftp://ftp.PostgreSQL.org/pub/</A>.</P> ftp://ftp.PostgreSQL.org/pub/</A>.</P>
<H3><A name="1.6">1.6</A>) What is the latest release?</H3> <H3 ID="1.6">1.6) What is the latest release?</H3>
<P>The latest release of PostgreSQL is version 8.1.1</P> <P>The latest release of PostgreSQL is version 8.1.1</P>
<P>We plan to have a major release every year, with minor releases <P>We plan to have a major release every year, with minor releases
every few months.</P> every few months.</P>
<H3><A name="1.7">1.7</A>) Where can I get support?</H3> <H3 ID="1.7">1.7) Where can I get support?</H3>
<P>The PostgreSQL community provides assistance to many of its users <P>The PostgreSQL community provides assistance to many of its users
via email. The main web site to subscribe to the email lists is via email. The main web site to subscribe to the email lists is
@ -243,7 +243,7 @@
"http://techdocs.postgresql.org/companies.php"> "http://techdocs.postgresql.org/companies.php">
http://techdocs.postgresql.org/companies.php</A>.</P> http://techdocs.postgresql.org/companies.php</A>.</P>
<H3><A name="1.8">1.8</A>) How do I submit a bug report?</H3> <H3 ID="1.8">1.8) How do I submit a bug report?</H3>
<P>Visit the PostgreSQL bug form at <A href= <P>Visit the PostgreSQL bug form at <A href=
"http://www.postgresql.org/support/submitbug"> "http://www.postgresql.org/support/submitbug">
@ -280,7 +280,7 @@
</li> </li>
</ul> </ul>
<H3><A name="1.9">1.9</A>) How do I find out about known bugs or <H3 ID="1.9">1.9) How do I find out about known bugs or
missing features?</H3> missing features?</H3>
<P>PostgreSQL supports an extended subset of <SMALL>SQL:2003</SMALL>. <P>PostgreSQL supports an extended subset of <SMALL>SQL:2003</SMALL>.
@ -312,7 +312,7 @@
Even the release notes do not contain every change made to the Even the release notes do not contain every change made to the
software.</P> software.</P>
<H3><A name="1.10">1.10</A>) What documentation is available?</H3> <H3 ID="1.10">1.10) What documentation is available?</H3>
<P>PostgreSQL includes extensive documentation, including a large <P>PostgreSQL includes extensive documentation, including a large
manual, manual pages, and some test examples. See the <I>/doc</I> manual, manual pages, and some test examples. See the <I>/doc</I>
@ -338,7 +338,7 @@
<P>Our web site contains even more documentation.</P> <P>Our web site contains even more documentation.</P>
<H3><A name="1.11">1.11</A>) How can I learn <H3 ID="1.11">1.11) How can I learn
<SMALL>SQL</SMALL>?</H3> <SMALL>SQL</SMALL>?</H3>
<P>First, consider the PostgreSQL-specific books mentioned above. <P>First, consider the PostgreSQL-specific books mentioned above.
@ -357,13 +357,13 @@
and at <A href= and at <A href=
"http://sqlcourse.com/">http://sqlcourse.com.</A></P> "http://sqlcourse.com/">http://sqlcourse.com.</A></P>
<H3><A name="1.12">1.12</A>) How do I join the development <H3 ID="1.12">1.12) How do I join the development
team?</H3> team?</H3>
<P>See the <a href="http://www.postgresql.org/docs/faqs.FAQ_DEV.html"> <P>See the <a href="http://www.postgresql.org/docs/faqs.FAQ_DEV.html">
Developer's FAQ</A>.</P> Developer's FAQ</A>.</P>
<H3><A name="1.13">1.13</A>) How does PostgreSQL compare to other <H3 ID="1.13">1.13) How does PostgreSQL compare to other
<SMALL>DBMS</SMALL>s?</H3> <SMALL>DBMS</SMALL>s?</H3>
<P>There are several ways of measuring software: features, <P>There are several ways of measuring software: features,
@ -427,7 +427,7 @@
<H2 align="center">User Client Questions</H2> <H2 align="center">User Client Questions</H2>
<H3><A name="2.1">2.1</A>) What interfaces are available for <H3 ID="2.1">2.1) What interfaces are available for
PostgreSQL?</H3> PostgreSQL?</H3>
<P>The PostgreSQL install includes only the <SMALL>C</SMALL> and embedded <P>The PostgreSQL install includes only the <SMALL>C</SMALL> and embedded
@ -442,7 +442,7 @@
in the <I>Drivers/Interfaces</I> section and via Internet search. in the <I>Drivers/Interfaces</I> section and via Internet search.
</P> </P>
<H3><A name="2.2">2.2</A>) What tools are available for using <H3 ID="2.2">2.2) What tools are available for using
PostgreSQL with Web pages?</H3> PostgreSQL with Web pages?</H3>
<P>A nice introduction to Database-backed Web pages can be seen at: <P>A nice introduction to Database-backed Web pages can be seen at:
@ -455,7 +455,7 @@
<P>For complex cases, many use the Perl and DBD::Pg with CGI.pm or <P>For complex cases, many use the Perl and DBD::Pg with CGI.pm or
mod_perl.</P> mod_perl.</P>
<H3><A name="2.3">2.3</A>) Does PostgreSQL have a graphical user <H3 ID="2.3">2.3) Does PostgreSQL have a graphical user
interface?</H3> interface?</H3>
<P>Yes, see <a href="http://techdocs.postgresql.org/guides/GUITools"> <P>Yes, see <a href="http://techdocs.postgresql.org/guides/GUITools">
@ -467,13 +467,13 @@
<H2 align="center">Administrative Questions</H2> <H2 align="center">Administrative Questions</H2>
<H3><A name="3.1">3.1</A>) How do I install PostgreSQL somewhere <H3 ID="3.1">3.1) How do I install PostgreSQL somewhere
other than <I>/usr/local/pgsql</I>?</H3> other than <I>/usr/local/pgsql</I>?</H3>
<P>Specify the <I>--prefix</I> option when running <P>Specify the <I>--prefix</I> option when running
<I>configure</I>.</P> <I>configure</I>.</P>
<H3><A name="3.2">3.2</A>) How do I control connections from other <H3 ID="3.2">3.2) How do I control connections from other
hosts?</H3> hosts?</H3>
<P>By default, PostgreSQL only allows connections from the local <P>By default, PostgreSQL only allows connections from the local
@ -483,7 +483,7 @@
host-based authentication by modifying the host-based authentication by modifying the
<I>$PGDATA/pg_hba.conf</I> file, and restart the server.</P> <I>$PGDATA/pg_hba.conf</I> file, and restart the server.</P>
<H3><A name="3.3">3.3</A>) How do I tune the database engine for <H3 ID="3.3">3.3) How do I tune the database engine for
better performance?</H3> better performance?</H3>
<P>There are three major areas for potential performance <P>There are three major areas for potential performance
@ -540,14 +540,14 @@
</DD> </DD>
</DL> </DL>
<H3><A name="3.4">3.4</A>) What debugging features are <H3 ID="3.4">3.4) What debugging features are
available?</H3> available?</H3>
<P>There are many <CODE>log_*</CODE> server configuration variables <P>There are many <CODE>log_*</CODE> server configuration variables
that enable printing of query and process statistics which can be that enable printing of query and process statistics which can be
very useful for debugging and performance measurements.</P> very useful for debugging and performance measurements.</P>
<H3><A name="3.5">3.5</A>) Why do I get <I>"Sorry, too many <H3 ID="3.5">3.5) Why do I get <I>"Sorry, too many
clients"</I> when trying to connect?</H3> clients"</I> when trying to connect?</H3>
<P>You have reached the default limit is 100 database sessions. You <P>You have reached the default limit is 100 database sessions. You
@ -556,7 +556,7 @@
<I>max_connections</I> value in <I>postgresql.conf</I> and <I>max_connections</I> value in <I>postgresql.conf</I> and
restarting the <I>postmaster</I>.</P> restarting the <I>postmaster</I>.</P>
<H3><A name="3.6">3.6</A>) Why do I need to do a dump and restore <H3 ID="3.6">3.6) Why do I need to do a dump and restore
to upgrade between major PostgreSQL releases?</H3> to upgrade between major PostgreSQL releases?</H3>
<P>The PostgreSQL team makes only small changes between minor releases, <P>The PostgreSQL team makes only small changes between minor releases,
@ -567,7 +567,7 @@
data in a generic format that can then be loaded in using the new internal data in a generic format that can then be loaded in using the new internal
format.</P> format.</P>
<H3><A name="3.7">3.7</A>) What computer hardware should I use?</H3> <H3 ID="3.7">3.7) What computer hardware should I use?</H3>
<P>Because PC hardware is mostly compatible, people tend to believe that <P>Because PC hardware is mostly compatible, people tend to believe that
all PC hardware is of equal quality. It is not. ECC RAM, SCSI, and all PC hardware is of equal quality. It is not. ECC RAM, SCSI, and
@ -581,7 +581,7 @@
<H2 align="center">Operational Questions</H2> <H2 align="center">Operational Questions</H2>
<H3><A name="4.1">4.1</A>) How do I <SMALL>SELECT</SMALL> only the <H3 ID="4.1">4.1) How do I <SMALL>SELECT</SMALL> only the
first few rows of a query? A random row?</H3> first few rows of a query? A random row?</H3>
<P>To retrieve only a few rows, if you know at the number of rows <P>To retrieve only a few rows, if you know at the number of rows
@ -600,7 +600,7 @@
LIMIT 1; LIMIT 1;
</PRE> </PRE>
<H3><A name="4.2">4.2</A>) How do I find out what tables, indexes, <H3 ID="4.2">4.2) How do I find out what tables, indexes,
databases, and users are defined? How do I see the queries used databases, and users are defined? How do I see the queries used
by <I>psql</I> to display them?</H3> by <I>psql</I> to display them?</H3>
@ -623,7 +623,7 @@
illustrates many of the <SMALL>SELECT</SMALL>s needed to get illustrates many of the <SMALL>SELECT</SMALL>s needed to get
information from the database system tables.</P> information from the database system tables.</P>
<H3><A name="4.3">4.3</A>) How do you change a column's data type?</H3> <H3 ID="4.3">4.3) How do you change a column's data type?</H3>
<P>Changing the data type of a column can be done easily in 8.0 <P>Changing the data type of a column can be done easily in 8.0
and later with <SMALL>ALTER TABLE ALTER COLUMN TYPE</SMALL>.</P> and later with <SMALL>ALTER TABLE ALTER COLUMN TYPE</SMALL>.</P>
@ -639,7 +639,7 @@
<P>You might then want to do <I>VACUUM FULL tab</I> to reclaim the <P>You might then want to do <I>VACUUM FULL tab</I> to reclaim the
disk space used by the expired rows.</P> disk space used by the expired rows.</P>
<H3><A name="4.4">4.4</A>) What is the maximum size for a row, a <H3 ID="4.4">4.4) What is the maximum size for a row, a
table, and a database?</H3> table, and a database?</H3>
<P>These are the limits:</P> <P>These are the limits:</P>
@ -676,7 +676,7 @@ table?</TD><TD>unlimited</TD></TR>
of an MD5 hash of the long column, and full text indexing of an MD5 hash of the long column, and full text indexing
allows for searching of words within the column.</P> allows for searching of words within the column.</P>
<H3><A name="4.5">4.5</A>) How much database disk space is required <H3 ID="4.5">4.5) How much database disk space is required
to store data from a typical text file?</H3> to store data from a typical text file?</H3>
<P>A PostgreSQL database may require up to five times the disk <P>A PostgreSQL database may require up to five times the disk
@ -713,7 +713,7 @@ table?</TD><TD>unlimited</TD></TR>
<P><SMALL>NULL</SMALL>s are stored as bitmaps, so they <P><SMALL>NULL</SMALL>s are stored as bitmaps, so they
use very little space.</P> use very little space.</P>
<H3><A name="4.6">4.6</A>) Why are my queries slow? Why don't they <H3 ID="4.6">4.6) Why are my queries slow? Why don't they
use my indexes?</H3> use my indexes?</H3>
<P>Indexes are not used by every query. Indexes are used only if the <P>Indexes are not used by every query. Indexes are used only if the
@ -777,12 +777,12 @@ table?</TD><TD>unlimited</TD></TR>
types exactly match the index's column types. This was particularly types exactly match the index's column types. This was particularly
true of int2, int8, and numeric column indexes.</P> true of int2, int8, and numeric column indexes.</P>
<H3><A name="4.7">4.7</A>) How do I see how the query optimizer is <H3 ID="4.7">4.7) How do I see how the query optimizer is
evaluating my query?</H3> evaluating my query?</H3>
<P>See the <SMALL>EXPLAIN</SMALL> manual page.</P> <P>See the <SMALL>EXPLAIN</SMALL> manual page.</P>
<H3><A name="4.8">4.8</A>) How do I perform regular expression <H3 ID="4.8">4.8) How do I perform regular expression
searches and case-insensitive regular expression searches? How do I searches and case-insensitive regular expression searches? How do I
use an index for case-insensitive searches?</H3> use an index for case-insensitive searches?</H3>
@ -809,7 +809,7 @@ table?</TD><TD>unlimited</TD></TR>
case to be stored in the column, use a <SMALL>CHECK</SMALL> case to be stored in the column, use a <SMALL>CHECK</SMALL>
constraint or a trigger.</P> constraint or a trigger.</P>
<H3><A name="4.9">4.9</A>) In a query, how do I detect if a field <H3 ID="4.9">4.9) In a query, how do I detect if a field
is <SMALL>NULL</SMALL>? How can I sort on whether a field is <SMALL> is <SMALL>NULL</SMALL>? How can I sort on whether a field is <SMALL>
NULL</SMALL> or not?</H3> NULL</SMALL> or not?</H3>
@ -833,7 +833,7 @@ table?</TD><TD>unlimited</TD></TR>
ORDER BY (col IS NOT NULL) ORDER BY (col IS NOT NULL)
</PRE> </PRE>
<H3><A name="4.10">4.10</A>) What is the difference between the <H3 ID="4.10">4.10) What is the difference between the
various character types?</H3> various character types?</H3>
<BLOCKQUOTE> <BLOCKQUOTE>
<TABLE> <TABLE>
@ -869,7 +869,7 @@ length</TD></TR>
particularly values that include <SMALL>NULL</SMALL> bytes. All the particularly values that include <SMALL>NULL</SMALL> bytes. All the
types described here have similar performance characteristics.</P> types described here have similar performance characteristics.</P>
<H3><A name="4.11.1">4.11.1</A>) How do I create a <H3 ID="4.11.1">4.11.1) How do I create a
serial/auto-incrementing field?</H3> serial/auto-incrementing field?</H3>
<P>PostgreSQL supports a <SMALL>SERIAL</SMALL> data type. It <P>PostgreSQL supports a <SMALL>SERIAL</SMALL> data type. It
@ -894,7 +894,7 @@ length</TD></TR>
See the <I>create_sequence</I> manual page for more information See the <I>create_sequence</I> manual page for more information
about sequences. about sequences.
<H3><A name="4.11.2">4.11.2</A>) How do I get the value of a <H3 ID="4.11.2">4.11.2) How do I get the value of a
<SMALL>SERIAL</SMALL> insert?</H3> <SMALL>SERIAL</SMALL> insert?</H3>
<P>One approach is to retrieve the next <SMALL>SERIAL</SMALL> value <P>One approach is to retrieve the next <SMALL>SERIAL</SMALL> value
@ -923,13 +923,13 @@ length</TD></TR>
new_id = execute("SELECT currval('person_id_seq')"); new_id = execute("SELECT currval('person_id_seq')");
</PRE> </PRE>
<H3><A name="4.11.3">4.11.3</A>) Doesn't <I>currval()</I> <H3 ID="4.11.3">4.11.3) Doesn't <I>currval()</I>
lead to a race condition with other users?</H3> lead to a race condition with other users?</H3>
<P>No. <I>currval()</I> returns the current value assigned by your <P>No. <I>currval()</I> returns the current value assigned by your
session, not by all sessions.</P> session, not by all sessions.</P>
<H3><A name="4.11.4">4.11.4</A>) Why aren't my sequence numbers <H3 ID="4.11.4">4.11.4) Why aren't my sequence numbers
reused on transaction abort? Why are there gaps in the numbering of reused on transaction abort? Why are there gaps in the numbering of
my sequence/SERIAL column?</H3> my sequence/SERIAL column?</H3>
@ -938,7 +938,7 @@ length</TD></TR>
completes. This causes gaps in numbering from aborted completes. This causes gaps in numbering from aborted
transactions.</P> transactions.</P>
<H3><A name="4.12">4.12</A>) What is an <SMALL>OID</SMALL>? What is <H3 ID="4.12">4.12) What is an <SMALL>OID</SMALL>? What is
a <SMALL>CTID</SMALL>?</H3> a <SMALL>CTID</SMALL>?</H3>
<P>Every row that is created in PostgreSQL gets a unique <P>Every row that is created in PostgreSQL gets a unique
@ -961,7 +961,7 @@ length</TD></TR>
are modified or reloaded. They are used by index entries to point are modified or reloaded. They are used by index entries to point
to physical rows.</P> to physical rows.</P>
<H3><A name="4.13">4.13</A>) Why do I get the error <I>"ERROR: <H3 ID="4.13">4.13) Why do I get the error <I>"ERROR:
Memory exhausted in AllocSetAlloc()"</I>?</H3> Memory exhausted in AllocSetAlloc()"</I>?</H3>
<P>You probably have run out of virtual memory on your system, <P>You probably have run out of virtual memory on your system,
@ -980,12 +980,12 @@ length</TD></TR>
backend is returning too much data, try it before starting the backend is returning too much data, try it before starting the
client. client.
<H3><A name="4.14">4.14</A>) How do I tell what PostgreSQL version <H3 ID="4.14">4.14) How do I tell what PostgreSQL version
I am running?</H3> I am running?</H3>
<P>From <I>psql</I>, type <CODE>SELECT version();</CODE></P> <P>From <I>psql</I>, type <CODE>SELECT version();</CODE></P>
<H3><A name="4.15">4.15</A>) How do I create a column that will <H3 ID="4.15">4.15) How do I create a column that will
default to the current time?</H3> default to the current time?</H3>
<P>Use <I>CURRENT_TIMESTAMP</I>:</P> <P>Use <I>CURRENT_TIMESTAMP</I>:</P>
@ -993,7 +993,7 @@ length</TD></TR>
CREATE TABLE test (x int, modtime TIMESTAMP DEFAULT CURRENT_TIMESTAMP ); CREATE TABLE test (x int, modtime TIMESTAMP DEFAULT CURRENT_TIMESTAMP );
</PRE> </PRE>
<H3><A name="4.16">4.16</A>) How do I perform an outer join?</H3> <H3 ID="4.16">4.16) How do I perform an outer join?</H3>
<P>PostgreSQL supports outer joins using the SQL standard syntax. <P>PostgreSQL supports outer joins using the SQL standard syntax.
Here are two examples:</P> Here are two examples:</P>
@ -1016,7 +1016,7 @@ length</TD></TR>
<SMALL>RIGHT</SMALL>, and <SMALL>FULL</SMALL> joins. Ordinary joins <SMALL>RIGHT</SMALL>, and <SMALL>FULL</SMALL> joins. Ordinary joins
are called <SMALL>INNER</SMALL> joins.</P> are called <SMALL>INNER</SMALL> joins.</P>
<H3><A name="4.17">4.17</A>) How do I perform queries using <H3 ID="4.17">4.17) How do I perform queries using
multiple databases?</H3> multiple databases?</H3>
<P>There is no way to query a database other than the current one. <P>There is no way to query a database other than the current one.
@ -1028,14 +1028,14 @@ length</TD></TR>
connections to different databases and merge the results on the connections to different databases and merge the results on the
client side.</P> client side.</P>
<H3><A name="4.18">4.18</A>) How do I return multiple rows or <H3 ID="4.18">4.18) How do I return multiple rows or
columns from a function?</H3> columns from a function?</H3>
<P>It is easy using set-returning functions, <P>It is easy using set-returning functions,
<a href="http://techdocs.postgresql.org/guides/SetReturningFunctions"> <a href="http://techdocs.postgresql.org/guides/SetReturningFunctions">
http://techdocs.postgresql.org/guides/SetReturningFunctions</a></P>. http://techdocs.postgresql.org/guides/SetReturningFunctions</a></P>.
<H3><A name="4.19">4.19</A>) Why do I get "relation with OID ##### <H3 ID="4.19">4.19) Why do I get "relation with OID #####
does not exist" errors when accessing temporary tables in PL/PgSQL does not exist" errors when accessing temporary tables in PL/PgSQL
functions?</H3> functions?</H3>
@ -1047,7 +1047,7 @@ length</TD></TR>
<SMALL>EXECUTE</SMALL> for temporary table access in PL/PgSQL. This <SMALL>EXECUTE</SMALL> for temporary table access in PL/PgSQL. This
will cause the query to be reparsed every time.</P> will cause the query to be reparsed every time.</P>
<H3><A name="4.20">4.20</A>) What replication solutions are available? <H3 ID="4.20">4.20) What replication solutions are available?
</H3> </H3>
<P>Though "replication" is a single term, there are several technologies <P>Though "replication" is a single term, there are several technologies
@ -1069,7 +1069,7 @@ length</TD></TR>
<P>There are also commercial and hardware-based replication solutions <P>There are also commercial and hardware-based replication solutions
available supporting a variety of replication models.</P> available supporting a variety of replication models.</P>
<H3><A name="4.21">4.21</A>) Why are my table and column names not <H3 ID="4.21">4.21) Why are my table and column names not
recognized in my query?</H3> recognized in my query?</H3>
<P>The most common cause is the use of double-quotes around table or <P>The most common cause is the use of double-quotes around table or

View File

@ -13,7 +13,7 @@
<H1>Developer's Frequently Asked Questions (FAQ) for <H1>Developer's Frequently Asked Questions (FAQ) for
PostgreSQL</H1> PostgreSQL</H1>
<P>Last updated: Thu Oct 27 09:48:14 EDT 2005</P> <P>Last updated: Tue Nov 22 10:13:04 EST 2005</P>
<P>Current maintainer: Bruce Momjian (<A href= <P>Current maintainer: Bruce Momjian (<A href=
"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR> "mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR>
@ -79,7 +79,7 @@
<H2>General Questions</H2> <H2>General Questions</H2>
<H3><A name="1.1">1.1</A>) How do I get involved in PostgreSQL <H3 ID="1.1">1.1) How do I get involved in PostgreSQL
development?</H3> development?</H3>
<P>Download the code and have a look around. See <A href= <P>Download the code and have a look around. See <A href=
@ -91,7 +91,7 @@
contributors and core members of the project discuss contributors and core members of the project discuss
development.</P> development.</P>
<H3><A name="1.2">1.2</A>) What development environment is required <H3 ID="1.2">1.2) What development environment is required
to develop code?</H3> to develop code?</H3>
<P>PostgreSQL is developed mostly in the C programming language. It <P>PostgreSQL is developed mostly in the C programming language. It
@ -123,7 +123,7 @@
when you make a modification to a C header file, all files depend when you make a modification to a C header file, all files depend
upon that file are also rebuilt.</P> upon that file are also rebuilt.</P>
<H3><A name="1.3">1.3</A>) What areas need work?</H3> <H3 ID="1.3">1.3) What areas need work?</H3>
Outstanding features are detailed in the TODO list. This is located Outstanding features are detailed in the TODO list. This is located
in <I>doc/TODO</I> in the source distribution or at <A href= in <I>doc/TODO</I> in the source distribution or at <A href=
"http://www.postgresql.org/docs/faqs.TODO.html"> "http://www.postgresql.org/docs/faqs.TODO.html">
@ -134,7 +134,7 @@
archives, the SQL standards and the recommend texts (see <A href= archives, the SQL standards and the recommend texts (see <A href=
"#1.10">1.10</A>).</P> "#1.10">1.10</A>).</P>
<H3><A name="1.4">1.4</A>) What do I do after choosing an item to <H3 ID="1.4">1.4) What do I do after choosing an item to
work on?</H3> work on?</H3>
<P>Send an email to pgsql-hackers with a proposal for what you want <P>Send an email to pgsql-hackers with a proposal for what you want
@ -154,7 +154,7 @@
<a href="http://momjian.postgresql.org/cgi-bin/pgpatches_hold"> <a href="http://momjian.postgresql.org/cgi-bin/pgpatches_hold">
http://momjian.postgresql.org/cgi-bin/pgpatches2</a>.</P> http://momjian.postgresql.org/cgi-bin/pgpatches2</a>.</P>
<H3><A name="1.5">1.5</A>) I've developed a patch, what next?</H3> <H3 ID="1.5">1.5) I've developed a patch, what next?</H3>
<P>Generate the patch in contextual diff format. If you are <P>Generate the patch in contextual diff format. If you are
unfamiliar with this, you might find the script unfamiliar with this, you might find the script
@ -174,7 +174,7 @@
that, let us know and we will manually update the documentation when that, let us know and we will manually update the documentation when
the patch is applied.</P> the patch is applied.</P>
<H3><A name="1.6">1.6</A>) Where can I learn more about the <H3 ID="1.6">1.6) Where can I learn more about the
code?</H3> code?</H3>
<P>Other than documentation in the source tree itself, you can find <P>Other than documentation in the source tree itself, you can find
@ -182,7 +182,7 @@
"http://www.postgresql.org/developer"> "http://www.postgresql.org/developer">
http://www.postgresql.org/developer</A>.</P> http://www.postgresql.org/developer</A>.</P>
<H3><A name="1.7">1.7</A>) How do I download/update the current <H3 ID="1.7">1.7) How do I download/update the current
source tree?</H3> source tree?</H3>
<P>There are several ways to obtain the source tree. Occasional <P>There are several ways to obtain the source tree. Occasional
@ -197,7 +197,7 @@
"http://developer.postgresql.org/docs/postgres/cvs.html"> "http://developer.postgresql.org/docs/postgres/cvs.html">
http://developer.postgresql.org/docs/postgres/cvs.html</A>.</P> http://developer.postgresql.org/docs/postgres/cvs.html</A>.</P>
<H3><A name="1.8">1.8</A>) How do I test my changes?</H3> <H3 ID="1.8">1.8) How do I test my changes?</H3>
<P><B>Basic system testing</B></P> <P><B>Basic system testing</B></P>
@ -245,7 +245,7 @@
you can use the <I>--enable-depend</I> option of <I>configure</I> you can use the <I>--enable-depend</I> option of <I>configure</I>
to have the compiler compute the dependencies automatically.</P> to have the compiler compute the dependencies automatically.</P>
<H3><A name="1.9">1.9</A>) What tools are available for <H3 ID="1.9">1.9) What tools are available for
developers?</H3> developers?</H3>
<P>First, all the files in the <I>src/tools</I> directory are <P>First, all the files in the <I>src/tools</I> directory are
@ -380,7 +380,7 @@
There is also a script called <I>unused_oids</I> in There is also a script called <I>unused_oids</I> in
<I>pgsql/src/include/catalog</I> that shows the unused oids.</P> <I>pgsql/src/include/catalog</I> that shows the unused oids.</P>
<H3><A name="1.10">1.10</A>) What books are good for <H3 ID="1.10">1.10) What books are good for
developers?</H3> developers?</H3>
<P>I have four good books, <I>An Introduction to Database <P>I have four good books, <I>An Introduction to Database
@ -394,7 +394,7 @@
on-line written by Jim Gray at <A href= on-line written by Jim Gray at <A href=
"http://www.benchmarkresources.com">http://www.benchmarkresources.com.</A>.</P> "http://www.benchmarkresources.com">http://www.benchmarkresources.com.</A>.</P>
<H3><A name="1.11">1.11</A>) What is configure all about?</H3> <H3 ID="1.11">1.11) What is configure all about?</H3>
<P>The files <I>configure</I> and <I>configure.in</I> are part of <P>The files <I>configure</I> and <I>configure.in</I> are part of
the GNU <I>autoconf</I> package. Configure allows us to test for the GNU <I>autoconf</I> package. Configure allows us to test for
@ -418,7 +418,7 @@
all files derived by configure are removed, so you see only the all files derived by configure are removed, so you see only the
file contained in the source distribution.</P> file contained in the source distribution.</P>
<H3><A name="1.12">1.12</A>) How do I add a new port?</H3> <H3 ID="1.12">1.12) How do I add a new port?</H3>
<P>There are a variety of places that need to be modified to add a <P>There are a variety of places that need to be modified to add a
new port. First, start in the <I>src/template</I> directory. Add an new port. First, start in the <I>src/template</I> directory. Add an
@ -437,7 +437,7 @@
handling. There is a <I>backend/port</I> directory if you need handling. There is a <I>backend/port</I> directory if you need
special files for your OS.</P> special files for your OS.</P>
<H3><A name="1.13">1.13</A>) Why don't you use threads, raw <H3 ID="1.13">1.13) Why don't you use threads, raw
devices, async-I/O, &lt;insert your favorite wizz-bang feature devices, async-I/O, &lt;insert your favorite wizz-bang feature
here&gt;?</H3> here&gt;?</H3>
@ -471,7 +471,7 @@
cautious about their adoption. The TODO list often contains links cautious about their adoption. The TODO list often contains links
to discussions showing our reasoning in these areas.</P> to discussions showing our reasoning in these areas.</P>
<H3><A name="1.14">1.14</A>) How are RPMs packaged?</H3> <H3 ID="1.14">1.14) How are RPMs packaged?</H3>
<P>This was written by Lamar Owen:</P> <P>This was written by Lamar Owen:</P>
@ -576,7 +576,7 @@
<P>Of course, there are many projects that DO include all the files <P>Of course, there are many projects that DO include all the files
necessary to build RPMs from their Official Tarball (TM).</P> necessary to build RPMs from their Official Tarball (TM).</P>
<H3><A name="1.15">1.15</A>) How are CVS branches managed?</H3> <H3 ID="1.15">1.15) How are CVS branches managed?</H3>
<P>This was written by Tom Lane:</P> <P>This was written by Tom Lane:</P>
@ -646,7 +646,7 @@
dot-release or two, so that we won't have to double-patch the first dot-release or two, so that we won't have to double-patch the first
wave of fixes.</P> wave of fixes.</P>
<H3><A name="1.16">1.16</A>) Where can I get a copy of the SQL <H3 ID="1.16">1.16) Where can I get a copy of the SQL
standards?</H3> standards?</H3>
<P>There are three versions of the SQL standard: SQL-92, SQL:1999, <P>There are three versions of the SQL standard: SQL-92, SQL:1999,
@ -683,7 +683,7 @@
(paper)</LI> (paper)</LI>
</UL> </UL>
<H3><A name="1.17">1.17</A>) Where can I get technical <H3 ID="1.17">1.17) Where can I get technical
assistance?</H3> assistance?</H3>
<P>Many technical questions held by those new to the code have been <P>Many technical questions held by those new to the code have been
@ -698,7 +698,7 @@
questions about development of new features, on IRC at questions about development of new features, on IRC at
irc.freenode.net in the #postgresql channel.</P> irc.freenode.net in the #postgresql channel.</P>
<H3><A name="1.18">1.18</A>) How do I get involved in PostgreSQL <H3 ID="1.18">1.18) How do I get involved in PostgreSQL
web site development?</H3> web site development?</H3>
<P>PostgreSQL website development is discussed on the <P>PostgreSQL website development is discussed on the
@ -714,7 +714,7 @@
<H2>Technical Questions</H2> <H2>Technical Questions</H2>
<H3><A name="2.1">2.1</A>) How do I efficiently access information <H3 ID="2.1">2.1) How do I efficiently access information
in tables from the backend code?</H3> in tables from the backend code?</H3>
<P>You first need to find the tuples(rows) you are interested in. <P>You first need to find the tuples(rows) you are interested in.
@ -782,7 +782,7 @@
<I>ReleaseBuffer()</I>, in the <I>heap_fetch()</I> case. Or it may <I>ReleaseBuffer()</I>, in the <I>heap_fetch()</I> case. Or it may
be a palloc'ed tuple, that you must <I>pfree()</I> when finished. be a palloc'ed tuple, that you must <I>pfree()</I> when finished.
<H3><A name="2.2">2.2</A>) Why are table, column, type, function, <H3 ID="2.2">2.2) Why are table, column, type, function,
view names sometimes referenced as <I>Name</I> or <I>NameData,</I> view names sometimes referenced as <I>Name</I> or <I>NameData,</I>
and sometimes as <I>char *?</I></H3> and sometimes as <I>char *?</I></H3>
@ -809,7 +809,7 @@
names(char *), there are many cases where Name and char * are used names(char *), there are many cases where Name and char * are used
interchangeably.</P> interchangeably.</P>
<H3><A name="2.3">2.3</A>) Why do we use <I>Node</I> and <H3 ID="2.3">2.3) Why do we use <I>Node</I> and
<I>List</I> to make data structures?</H3> <I>List</I> to make data structures?</H3>
<P>We do this because this allows a consistent way to pass data <P>We do this because this allows a consistent way to pass data
@ -902,7 +902,7 @@
The output appears in the postmaster log file, or on your screen if The output appears in the postmaster log file, or on your screen if
you are running a backend directly without a postmaster. you are running a backend directly without a postmaster.
<H3><A name="2.4">2.4</A>) I just added a field to a structure. <H3 ID="2.4">2.4) I just added a field to a structure.
What else should I do?</H3> What else should I do?</H3>
<P>The structures passing around from the parser, rewrite, <P>The structures passing around from the parser, rewrite,
@ -914,7 +914,7 @@
places the structure might need code for your new field. <I>mkid</I> places the structure might need code for your new field. <I>mkid</I>
is helpful with this (see <A href="#1.9">1.9</A>).</P> is helpful with this (see <A href="#1.9">1.9</A>).</P>
<H3><A name="2.5">2.5</A>) Why do we use <I>palloc</I>() and <H3 ID="2.5">2.5) Why do we use <I>palloc</I>() and
<I>pfree</I>() to allocate memory?</H3> <I>pfree</I>() to allocate memory?</H3>
<P><I>palloc()</I> and <I>pfree()</I> are used in place of malloc() <P><I>palloc()</I> and <I>pfree()</I> are used in place of malloc()
@ -925,7 +925,7 @@
memory can be allocated in. These affect when the allocated memory memory can be allocated in. These affect when the allocated memory
is freed by the backend.</P> is freed by the backend.</P>
<H3><A name="2.6">2.6</A>) What is ereport()?</H3> <H3 ID="2.6">2.6) What is ereport()?</H3>
<P><I>ereport()</I> is used to send messages to the front-end, and <P><I>ereport()</I> is used to send messages to the front-end, and
optionally terminate the current query being processed. The first optionally terminate the current query being processed. The first
@ -944,7 +944,7 @@
descriptors so you don't need to clean these up before the descriptors so you don't need to clean these up before the
call.</P> call.</P>
<H3><A name="2.7">2.7</A>) What is CommandCounterIncrement()?</H3> <H3 ID="2.7">2.7) What is CommandCounterIncrement()?</H3>
<P>Normally, transactions can not see the rows they modify. This <P>Normally, transactions can not see the rows they modify. This
allows <CODE>UPDATE foo SET x = x + 1</CODE> to work correctly.</P> allows <CODE>UPDATE foo SET x = x + 1</CODE> to work correctly.</P>
@ -957,7 +957,7 @@
increments the Command Counter, creating a new part of the increments the Command Counter, creating a new part of the
transaction.</P> transaction.</P>
<H3><A name="2.8">2.8</A>) What debugging features are <H3 ID="2.8">2.8) What debugging features are
available?</H3> available?</H3>
<P>First, try running <I>configure</I> with the --enable-cassert <P>First, try running <I>configure</I> with the --enable-cassert