-<REFENTRY ID="SQL-LOCK">
- <REFMETA>
- <REFENTRYTITLE>
+<refentry id="SQL-LOCK">
+ <refmeta>
+ <refentrytitle>
LOCK
- </REFENTRYTITLE>
- <REFMISCINFO>SQL - Language Statements</REFMISCINFO>
- </REFMETA>
- <REFNAMEDIV>
- <REFNAME>
+ </refentrytitle>
+ <refmiscinfo>SQL - Language Statements</refmiscinfo>
+ </refmeta>
+ <refnamediv>
+ <refname>
LOCK
- </REFNAME>
- <REFPURPOSE>
+ </refname>
+ <refpurpose>
Explicit lock of a table inside a transaction
- </REFPURPOSE>
+ </refpurpose>
</refnamediv>
- <REFSYNOPSISDIV>
- <REFSYNOPSISDIVINFO>
- <DATE>1998-09-24</DATE>
- </REFSYNOPSISDIVINFO>
- <SYNOPSIS>
- LOCK [ TABLE ] [IN [ROW|ACCESS] [SHARE|EXCLUSIVE] | [SHARE ROW EXCLUSIVE] MODE]
- <REPLACEABLE CLASS="PARAMETER">table</REPLACEABLE>
- </SYNOPSIS>
+ <refsynopsisdiv>
+ <refsynopsisdivinfo>
+ <date>1998-09-24</date>
+ </refsynopsisdivinfo>
+ <synopsis>
+LOCK [ TABLE ] <replaceable class="PARAMETER">table</replaceable>
+LOCK [ TABLE ] <replaceable class="PARAMETER">table</replaceable> IN [ ROW | ACCESS ] { SHARE | EXCLUSIVE } MODE
+LOCK [ TABLE ] <replaceable class="PARAMETER">table</replaceable> IN SHARE ROW EXCLUSIVE MODE
+ </synopsis>
- <REFSECT2 ID="R2-SQL-LOCK-1">
- <REFSECT2INFO>
- <DATE>1998-09-01</DATE>
- </REFSECT2INFO>
- <TITLE>
+ <refsect2 id="R2-SQL-LOCK-1">
+ <refsect2info>
+ <date>1998-09-01</date>
+ </refsect2info>
+ <title>
Inputs
- </TITLE>
- <PARA>
- </PARA>
- <VARIABLELIST>
- <VARLISTENTRY>
- <TERM>
- <REPLACEABLE CLASS="PARAMETER">table</REPLACEABLE>
- </TERM>
- <LISTITEM>
- <PARA>
- The name of an existing table to lock.
- </para>
- </listitem>
- </varlistentry>
- </VARIABLELIST>
-
- </REFSECT2>
+ </title>
+ <para>
+
+ <variablelist>
+ <varlistentry>
+ <term>
+ <replaceable class="PARAMETER">table</replaceable>
+ </term>
+ <listitem>
+ <para>
+ The name of an existing table to lock.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
+ SHARE MODE
+ </term>
+ <listitem>
+ <para>
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
+ EXCLUSIVE MODE
+ </term>
+ <listitem>
+ <para>
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
+ ROW SHARE MODE
+ </term>
+ <listitem>
+ <para>
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
+ ROW EXCLUSIVE MODE
+ </term>
+ <listitem>
+ <para>
+ </para>
+ </listitem>
+ </varlistentry>
- <REFSECT2 ID="R2-SQL-LOCK-2">
- <REFSECT2INFO>
- <DATE>1998-09-24</DATE>
- </REFSECT2INFO>
- <TITLE>
+ <varlistentry>
+ <term>
+ ACCESS SHARE MODE
+ </term>
+ <listitem>
+ <para>
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
+ ACCESS EXCLUSIVE MODE
+ </term>
+ <listitem>
+ <para>
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
+ SHARE ROW EXCLUSIVE MODE
+ </term>
+ <listitem>
+ <para>
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </para>
+ </refsect2>
+
+ <refsect2 id="R2-SQL-LOCK-2">
+ <refsect2info>
+ <date>1998-09-24</date>
+ </refsect2info>
+ <title>
Outputs
- </TITLE>
- <PARA>
+ </title>
+ <para>
- <VARIABLELIST>
- <TERM>
- ERROR <REPLACEABLE CLASS="PARAMETER">table</REPLACEABLE>: Table does not exist.
- </TERM>
- <LISTITEM>
- <PARA>
- Message returned if <REPLACEABLE CLASS="PARAMETER">table</REPLACEABLE>
+ <variablelist>
+ <varlistentry>
+ <term>
+ ERROR <replaceable class="PARAMETER">table</replaceable>: Table does not exist.
+ </term>
+ <listitem>
+ <para>
+ Message returned if <replaceable class="PARAMETER">table</replaceable>
does not exist.
</para>
</listitem>
</varlistentry>
- </VARIABLELIST>
+ </variablelist>
</para>
- </REFSECT2>
- </REFSYNOPSISDIV>
+ </refsect2>
+ </refsynopsisdiv>
- <REFSECT1 ID="R1-SQL-LOCK-1">
- <REFSECT1INFO>
- <DATE>1998-09-24</DATE>
- </REFSECT1INFO>
- <TITLE>
+ <refsect1 id="R1-SQL-LOCK-1">
+ <refsect1info>
+ <date>1998-09-24</date>
+ </refsect1info>
+ <title>
Description
- </TITLE>
- <PARA>
+ </title>
+ <para>
By default, <command>LOCK</command> locks in exclusive mode a table inside
a transaction. Various options allow shared access, or row-level locking
control. The classic use for this is
</para>
</note>
- <REFSECT2 ID="R2-SQL-LOCK-3">
- <REFSECT2INFO>
- <DATE>1998-09-24</DATE>
- </REFSECT2INFO>
- <TITLE>
+ <refsect2 id="R2-SQL-LOCK-3">
+ <refsect2info>
+ <date>1998-09-24</date>
+ </refsect2info>
+ <title>
Notes
- </TITLE>
+ </title>
<para>
<command>LOCK</command> is a <productname>Postgres</productname>
language extension.
</para>
</note>
</para>
- </REFSECT2>
+ </refsect2>
</refsect1>
- <REFSECT1 ID="R1-SQL-LOCK-2">
- <TITLE>
+ <refsect1 id="R1-SQL-LOCK-2">
+ <title>
Usage
- </TITLE>
- <PARA>
- </PARA>
- <ProgramListing>
+ </title>
+ <para>
+ </para>
+ <programlisting>
--Explicit locking to prevent deadlock:
--
BEGIN WORK;
UPDATE films SET len = INTERVAL '100 minute'
WHERE len = INTERVAL '117 minute';
COMMIT WORK;
- </ProgramListing>
+ </programlisting>
- </REFSECT1>
+ </refsect1>
- <REFSECT1 ID="R1-SQL-LOCK-3">
- <TITLE>
+ <refsect1 id="R1-SQL-LOCK-3">
+ <title>
Compatibility
- </TITLE>
+ </title>
- <REFSECT2 ID="R2-SQL-LOCK-4">
- <REFSECT2INFO>
- <DATE>1998-09-24</DATE>
- </REFSECT2INFO>
- <TITLE>
+ <refsect2 id="R2-SQL-LOCK-4">
+ <refsect2info>
+ <date>1998-09-24</date>
+ </refsect2info>
+ <title>
SQL92
- </TITLE>
- <PARA>
+ </title>
+ <para>
There is no <command>LOCK TABLE</command> in <acronym>SQL92</acronym>,
which instead uses <command>SET TRANSACTION</command> to specify
concurrency level on transactions. We support that too.
</para>
</refsect2>
</refsect1>
-</REFENTRY>
+</refentry>
<!-- Keep this comment at the end of the file
Local variables:
-<REFENTRY ID="SQL-SET">
- <REFMETA>
- <REFENTRYTITLE>
+<refentry id="SQL-SET">
+ <refmeta>
+ <refentrytitle>
SET
- </REFENTRYTITLE>
- <REFMISCINFO>SQL - Language Statements</REFMISCINFO>
- </REFMETA>
- <REFNAMEDIV>
- <REFNAME>
+ </refentrytitle>
+ <refmiscinfo>SQL - Language Statements</refmiscinfo>
+ </refmeta>
+ <refnamediv>
+ <refname>
SET
- </REFNAME>
- <REFPURPOSE>
+ </refname>
+ <refpurpose>
Set run-time parameters for session
- </REFPURPOSE>
+ </refpurpose>
</refnamediv>
- <REFSYNOPSISDIV>
- <REFSYNOPSISDIVINFO>
- <DATE>1998-09-24</DATE>
- </REFSYNOPSISDIVINFO>
- <SYNOPSIS>
-SET <REPLACEABLE CLASS="PARAMETER">variable</REPLACEABLE> { TO | = } { '<REPLACEABLE CLASS="PARAMETER">value</REPLACEABLE>' | DEFAULT }
-SET TIME ZONE { '<REPLACEABLE CLASS="PARAMETER">timezone</REPLACEABLE>' | LOCAL };
- </SYNOPSIS>
+ <refsynopsisdiv>
+ <refsynopsisdivinfo>
+ <date>1998-09-24</date>
+ </refsynopsisdivinfo>
+ <synopsis>
+SET <replaceable class="PARAMETER">variable</replaceable> { TO | = } { '<replaceable class="PARAMETER">value</replaceable>' | DEFAULT }
+SET TIME ZONE { '<replaceable class="PARAMETER">timezone</replaceable>' | LOCAL | DEFAULT };
+SET TRANSACTION ISOLATION LEVEL { READ COMMITTED | SERIALIZED | DEFAULT }
+ </synopsis>
- <REFSECT2 ID="R2-SQL-SET-1">
- <REFSECT2INFO>
- <DATE>1998-09-24</DATE>
- </REFSECT2INFO>
- <TITLE>
+ <refsect2 id="R2-SQL-SET-1">
+ <refsect2info>
+ <date>1998-09-24</date>
+ </refsect2info>
+ <title>
Inputs
- </TITLE>
- <PARA>
+ </title>
+ <para>
- <VARIABLELIST>
- <VARLISTENTRY>
- <TERM>
- <REPLACEABLE CLASS="PARAMETER">variable</REPLACEABLE>
- </TERM>
- <LISTITEM>
+ <variablelist>
+ <varlistentry>
+ <term>
+ <replaceable class="PARAMETER">variable</replaceable>
+ </term>
+ <listitem>
<para>
Settable global parameter.
</para>
</varlistentry>
<varlistentry>
<term>
- <REPLACEABLE CLASS="PARAMETER">value</REPLACEABLE>
+ <replaceable class="PARAMETER">value</replaceable>
</term>
<listitem>
- <PARA>
+ <para>
New value of parameter.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
+
<para>
The possible variables and allowed values are:
- <VARIABLELIST>
- <VARLISTENTRY>
- <TERM>
- DateStyle
- </TERM>
- <LISTITEM>
- <PARA>
+ <variablelist>
+ <varlistentry>
+ <term>
+ CLIENT_ENCODING | NAMES
+ </term>
+ <listitem>
+ <para>
+ Sets the multi-byte client encoding
- <VARIABLELIST>
- <VARLISTENTRY>
- <TERM>
+ <variablelist>
+ <varlistentry>
+ <term>
+ <replaceable class="parameter">value</replaceable>
+ </term>
+ <listitem>
+ <para>
+ Sets the multi-byte client encoding to
+ <replaceable class="parameter">value</replaceable>.
+ The specified encoding must be supported by the backend.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
+ DEFAULT
+ </term>
+ <listitem>
+ <para>
+ Sets the multi-byte client encoding.
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </para>
+
+ <para>
+ This is only enabled if multi-byte was specified to configure.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
+ DateStyle
+ </term>
+ <listitem>
+ <para>
+ <variablelist>
+ <varlistentry>
+ <term>
ISO
- </TERM>
- <LISTITEM>
- <PARA>
+ </term>
+ <listitem>
+ <para>
use ISO 8601-style dates and times
</para>
</listitem>
</varlistentry>
- <VARLISTENTRY>
- <TERM>
+ <varlistentry>
+ <term>
SQL
- </TERM>
- <LISTITEM>
- <PARA>
+ </term>
+ <listitem>
+ <para>
use Oracle/Ingres-style dates and times
</para>
</listitem>
</varlistentry>
- <VARLISTENTRY>
- <TERM>
+ <varlistentry>
+ <term>
Postgres
- </TERM>
- <LISTITEM>
- <PARA>
+ </term>
+ <listitem>
+ <para>
use traditional <productname>Postgres</productname> format
</para>
</listitem>
</varlistentry>
- <VARLISTENTRY>
- <TERM>
+ <varlistentry>
+ <term>
European
- </TERM>
- <LISTITEM>
- <PARA>
+ </term>
+ <listitem>
+ <para>
use dd/mm/yyyy for numeric date representations.
</para>
</listitem>
</varlistentry>
- <VARLISTENTRY>
- <TERM>
+ <varlistentry>
+ <term>
NonEuropean
- </TERM>
- <LISTITEM>
- <PARA>
+ </term>
+ <listitem>
+ <para>
use mm/dd/yyyy for numeric date representations.
</para>
</listitem>
</varlistentry>
- <VARLISTENTRY>
- <TERM>
+ <varlistentry>
+ <term>
German
- </TERM>
- <LISTITEM>
- <PARA>
+ </term>
+ <listitem>
+ <para>
use dd.mm.yyyy for numeric date representations.
</para>
</listitem>
</varlistentry>
- <VARLISTENTRY>
- <TERM>
+ <varlistentry>
+ <term>
US
- </TERM>
- <LISTITEM>
- <PARA>
+ </term>
+ <listitem>
+ <para>
same as 'NonEuropean'
</para>
</listitem>
</varlistentry>
- <VARLISTENTRY>
- <TERM>
+ <varlistentry>
+ <term>
default
- </TERM>
- <LISTITEM>
- <PARA>
+ </term>
+ <listitem>
+ <para>
restores the default values ('US,Postgres')
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
+
+ <para>
+ Date format initialization my be done by:
+ <simplelist>
+ <member>
+ Setting PGDATESTYLE environment variable.
+ </member>
+ <member>
+ Running postmaster using -oe parameter to set
+ dates to the 'European' convention.
+ Note that this affects only the some combinations of date styles; for example
+ the ISO style is not affected by this parameter.
+ </member>
+ <member>
+ Changing variables in
+ <filename>src/backend/utils/init/globals.c</filename>.
+ </member>
+ </simplelist>
+ </para>
+ <para>
+ The variables in <filename>globals.c</filename> which can be changed are:
+ <simplelist>
+ <member>
+ bool EuroDates = false | true
+ </member>
+ <member>
+ int DateStyle = USE_ISO_DATES | USE_POSTGRES_DATES | USE_SQL_DATES | USE_GERMAN_DATES
+ </member>
+ </simplelist>
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
+ SERVER_ENCODING
+ </term>
+ <listitem>
+ <para>
+ Sets the multi-byte server encoding
+
+ <variablelist>
+ <varlistentry>
+ <term>
+ <replaceable class="parameter">value</replaceable>
+ </term>
+ <listitem>
+ <para>
+ Sets the multi-byte server encoding.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
+ DEFAULT
+ </term>
+ <listitem>
+ <para>
+ Sets the multi-byte server encoding.
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </para>
+ <para>
+ This is only enabled if multi-byte was specified to configure.
+ </para>
</listitem>
</varlistentry>
- </variablelist>
- </para>
- <para>
- Date format initialization my be done by:
- <simplelist>
- <member>
- Setting PGDATESTYLE environment variable.
- </member>
- <member>
- Running postmaster using -oe parameter to set
- dates to the 'European' convention.
- Note that this affects only the some combinations of date styles; for example
- the ISO style is not affected by this parameter.
- </member>
- <member>
- Changing variables in
- <filename>src/backend/utils/init/globals.c</filename>.
- </member>
- </simplelist>
- </para>
- <para>
- The variables in <filename>globals.c</filename> which can be changed are:
- <simplelist>
- <member>
- bool EuroDates = false | true
- </member>
- <member>
- int DateStyle = USE_ISO_DATES | USE_POSTGRES_DATES | USE_SQL_DATES | USE_GERMAN_DATES
- </member>
- </simplelist>
- </para>
- <para>
- <variablelist>
<varlistentry>
<term>
TIMEZONE
</para>
</listitem>
</varlistentry>
+
+ <varlistentry>
+ <term>
+ TRANSACTION ISOLATION LEVEL
+ </term>
+ <listitem>
+ <para>
+ Sets the isolation level for the current transaction.
+
+ <variablelist>
+ <varlistentry>
+ <term>
+ READ COMMITTED
+ </term>
+ <listitem>
+ <para>
+ The current transaction reads only
+ committed rows. READ COMMITTED is the default.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
+ SERIALIZABLE
+ </term>
+ <listitem>
+ <para>
+ The current transaction will place a
+ lock on every row read, so later reads in that transaction
+ see the rows unmodified by other transactions.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
+ DEFAULT
+ </term>
+ <listitem>
+ <para>
+ Sets the isolation level for the current transaction to
+ <option>READ COMMITTED</option>.
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </para>
+ </listitem>
+ </varlistentry>
</variablelist>
</para>
+
<para>
There are also several internal or optimization
parameters which can be specified
The frontend may be initialized by setting the PGCOSTHEAP
environment variable.
</para>
- <variablelist>
- <varlistentry>
- <term>
- COST_INDEX
- </term>
- <listitem>
- <para>
- Sets the default cost of an index scan for use by the optimizer.
- </para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
- <term>
- <replaceable class="parameter">float4</replaceable>
- </term>
- <listitem>
- <para>
- Set the cost of an index scan to the specified floating point value.
- </para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
- <term>
- DEFAULT
- </term>
- <listitem>
- <para>
- Sets the cost of an index scan to the default value.
- </para>
- </listitem>
- </varlistentry>
- </variablelist>
- </listitem>
- </varlistentry>
- </variablelist>
- </para>
- <para>
- The frontend may be initialized by setting the PGCOSTINDEX
- environment variable.
-
- <variablelist>
- <varlistentry>
- <term>
- GEQO
- </term>
- <listitem>
- <para>
- Sets the threshold for using the genetic optimizer algorithm.
- </para>
-
- <variablelist>
- <varlistentry>
- <term>
- On
- </term>
- <listitem>
- <para>
- enables the genetic optimizer algorithm
- for statements with 6 or more tables.
- </para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term>
- On=<replaceable class="parameter">#</replaceable>
- </term>
- <listitem>
- <para>
- Takes an integer argument to enable the genetic optimizer algorithm
- for statements with <replaceable class="parameter">#</replaceable>
- or more tables in the query.
- </para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term>
- Off
- </term>
- <listitem>
- <para>
- disables the genetic optimizer algorithm.
- </para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term>
- DEFAULT
- </term>
- <listitem>
- <para>
- Equivalent to specifying <command>SET GEQO='on'</command>
- </para>
- </listitem>
- </varlistentry>
- </variablelist>
</listitem>
</varlistentry>
- </variablelist>
- </para>
- <para>
- This algorithm is on by default, which used GEQO for
- statements of eleven or more tables.
- (See the chapter on GEQO in the Programmer's Guide
- for more information).
- </para>
- <para>
- The frontend may be initialized by setting PGGEQO
- environment variable.
- </para>
- <para>
- It may be useful when joining big relations with
- small ones. This algorithm is off by default.
- It's not used by GEQO anyway.
-
- <variablelist>
- <varlistentry>
- <term>
- KSQO
- </term>
- <listitem>
- <para>
- <firstterm>Key Set Query Optimizer</firstterm> forces the query optimizer
- to optimize repetative OR clauses such as generated by
- <productname>MicroSoft Access</productname>:
- </para>
-
- <variablelist>
- <varlistentry>
- <term>
- On
- </term>
- <listitem>
- <para>
- enables this optimization.
- </para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
- <term>
- Off
- </term>
- <listitem>
- <para>
- disables this optimization.
- </para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
- <term>
- DEFAULT
- </term>
- <listitem>
- <para>
- Equivalent to specifying <command>SET KSQO='off'</command>.
- </para>
- </listitem>
- </varlistentry>
- </variablelist>
- </listitem>
- </varlistentry>
- </variablelist>
- </para>
- <para>
- It may be useful when joining big relations with
- small ones. This algorithm is off by default.
- It's not used by GEQO anyway.
- </para>
- <para>
- The frontend may be initialized by setting the PGKSQO
- environment variable.
- <variablelist>
+
<varlistentry>
<term>
- QUERY_LIMIT
+ COST_INDEX
</term>
<listitem>
<para>
- Sets the number of rows returned by a query.
+ Sets the default cost of an index scan for use by the optimizer.
+
+ <variablelist>
+ <varlistentry>
+ <term>
+ <replaceable class="parameter">float4</replaceable>
+ </term>
+ <listitem>
+ <para>
+ Set the cost of an index scan to the specified floating point value.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
+ DEFAULT
+ </term>
+ <listitem>
+ <para>
+ Sets the cost of an index scan to the default value.
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
</para>
-
- <variablelist>
- <varlistentry>
- <term>
- Value
- </term>
- <listitem>
- <para>
- Maximum number of rows to return for a query. The default is to allow
- an unlimited number of rows.
- </para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term>
- <replaceable class="parameter">#</replaceable>
- </term>
- <listitem>
- <para>
- Sets the maximum number of rows returned by a
- query to <replaceable class="parameter">#</replaceable>.
- </para>
- </listitem>
- </varlistentry>
- <varlistentry>
- <term>
- DEFAULT
- </term>
- <listitem>
- <para>
- Sets the maximum number of rows returned by a query to be unlimited.
- </para>
- </listitem>
- </varlistentry>
- </variablelist>
+
<para>
- By default, there is no limit to the number of rows
- returned by a query.
+ The frontend may be initialized by setting the PGCOSTINDEX
+ environment variable.
</para>
</listitem>
</varlistentry>
- </variablelist>
- <variablelist>
<varlistentry>
<term>
- TRANSACTION ISOLATION LEVEL
+ GEQO
</term>
<listitem>
<para>
- Sets the isolation level for the current transaction.
-
+ Sets the threshold for using the genetic optimizer algorithm.
+
<variablelist>
<varlistentry>
<term>
- <replaceable class="parameter">value</replaceable>
+ ON
</term>
<listitem>
<para>
- Sets the isolation level for the current transaction to
- 'SERIALIZABLE' or 'READ COMMITTED'.
- SERIALIZABLE means that the current transaction will place a
- lock on every row read, so later reads in that transaction
- see the rows unmodified by other transactions.
- READ COMMITTED means that the current transaction reads only
- committed rows. READ COMMITTED is the default.
+ enables the genetic optimizer algorithm
+ for statements with 6 or more tables.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>
+ ON=<replaceable class="parameter">#</replaceable>
+ </term>
+ <listitem>
+ <para>
+ Takes an integer argument to enable the genetic optimizer algorithm
+ for statements with <replaceable class="parameter">#</replaceable>
+ or more tables in the query.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term>
+ OFF
+ </term>
+ <listitem>
+ <para>
+ disables the genetic optimizer algorithm.
</para>
</listitem>
</varlistentry>
- </para>
-
<varlistentry>
<term>
DEFAULT
</term>
<listitem>
<para>
- Sets the isolation level for the current transaction to
- 'READ COMMITTED'.
+ Equivalent to specifying <command>SET GEQO='ON'</command>
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
- <variablelist>
+ <para>
+ This algorithm is on by default, which used GEQO for
+ statements of eleven or more tables.
+ (See the chapter on GEQO in the Programmer's Guide
+ for more information).
+ </para>
+ <para>
+ The frontend may be initialized by setting PGGEQO
+ environment variable.
+ </para>
+ <para>
+ It may be useful when joining big relations with
+ small ones. This algorithm is off by default.
+ It's not used by GEQO anyway.
+ </para>
+ </listitem>
+ </varlistentry>
+
<varlistentry>
<term>
- CLIENT_ENCODING | NAMES
+ KSQO
</term>
<listitem>
<para>
- Sets the multi-byte client encoding
-
+ <firstterm>Key Set Query Optimizer</firstterm> forces the query optimizer
+ to optimize repetative OR clauses such as generated by
+ <productname>MicroSoft Access</productname>:
+
<variablelist>
<varlistentry>
<term>
- <replaceable class="parameter">value</replaceable>
+ ON
</term>
<listitem>
<para>
- Sets the multi-byte client encoding.
+ enables this optimization.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>
+ OFF
+ </term>
+ <listitem>
+ <para>
+ disables this optimization.
</para>
</listitem>
</varlistentry>
- </para>
<varlistentry>
<term>
</term>
<listitem>
<para>
- Sets the multi-byte client encoding.
+ Equivalent to specifying <command>SET KSQO='OFF'</command>.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
+
<para>
- This is only enabled if multi-byte was specified to configure.
+ It may be useful when joining big relations with
+ small ones. This algorithm is off by default.
+ It's not used by GEQO anyway.
</para>
+ <para>
+ The frontend may be initialized by setting the PGKSQO
+ environment variable.
+ </para>
+ </listitem>
+ </varlistentry>
- <variablelist>
<varlistentry>
<term>
- SERVER_ENCODING
+ QUERY_LIMIT
</term>
<listitem>
<para>
- Sets the multi-byte server encoding
-
+ Sets the maximum number of rows returned by a query.
+ By default, there is no limit to the number of rows
+ returned by a query.
+
<variablelist>
<varlistentry>
<term>
- <replaceable class="parameter">value</replaceable>
+ <replaceable class="parameter">#</replaceable>
</term>
<listitem>
<para>
- Sets the multi-byte server encoding.
+ Sets the maximum number of rows returned by a
+ query to <replaceable class="parameter">#</replaceable>.
</para>
</listitem>
</varlistentry>
- </para>
-
<varlistentry>
<term>
DEFAULT
</term>
<listitem>
<para>
- Sets the multi-byte server encoding.
+ Sets the maximum number of rows returned by a query to be unlimited.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
- <para>
- This is only enabled if multi-byte was specified to configure.
- </para>
-
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </para>
+ </refsect2>
- </REFSECT2>
-
- <REFSECT2 ID="R2-SQL-SET-2">
- <REFSECT2INFO>
- <DATE>1998-09-24</DATE>
- </REFSECT2INFO>
- <TITLE>
+ <refsect2 id="R2-SQL-SET-2">
+ <refsect2info>
+ <date>1998-09-24</date>
+ </refsect2info>
+ <title>
Outputs
- </TITLE>
- <PARA>
+ </title>
+ <para>
- <VARIABLELIST>
- <VARLISTENTRY>
- <TERM>
+ <variablelist>
+ <varlistentry>
+ <term>
<returnvalue>SET VARIABLE</returnvalue>
- </TERM>
- <LISTITEM>
- <PARA>
+ </term>
+ <listitem>
+ <para>
Message returned if successfully.
</para>
</listitem>
</varlistentry>
- <VARLISTENTRY>
- <TERM>
- <returnvalue>WARN: Bad value for <replaceable class="parameter">variable</replaceable> (<replaceable class="parameter">value</replaceable>)</returnvalue>
- </TERM>
- <LISTITEM>
- <PARA>
- If the command fails to set variable.
+ <varlistentry>
+ <term>
+ <returnvalue>WARN: Bad value for
+ <replaceable class="parameter">variable</replaceable>
+ (<replaceable class="parameter">value</replaceable>)</returnvalue>
+ </term>
+ <listitem>
+ <para>
+ If the command fails to set the specified variable.
</para>
</listitem>
</varlistentry>
- </VARIABLELIST>
+ </variablelist>
</para>
- </REFSECT2>
- </REFSYNOPSISDIV>
+ </refsect2>
+ </refsynopsisdiv>
- <REFSECT1 ID="R1-SQL-SET-1">
- <REFSECT1INFO>
- <DATE>1998-09-24</DATE>
- </REFSECT1INFO>
- <TITLE>
+ <refsect1 id="R1-SQL-SET-1">
+ <refsect1info>
+ <date>1998-09-24</date>
+ </refsect1info>
+ <title>
Description
- </TITLE>
- <PARA>
+ </title>
+ <para>
<command>SET</command> will modify configuration parameters for variable during
a session.
</para>
<para>
<command>SET TIME ZONE</command> changes the session's
default time zone offset.
- A SQL-session always begins with an initial default time zone
+ An SQL-session always begins with an initial default time zone
offset.
The <command>SET TIME ZONE</command> statement is used to change the default
time zone offset for the current SQL session.
</para>
- <REFSECT2 ID="R2-SQL-SET-3">
- <REFSECT2INFO>
- <DATE>1998-09-24</DATE>
- </REFSECT2INFO>
- <TITLE>
+ <refsect2 id="R2-SQL-SET-3">
+ <refsect2info>
+ <date>1998-09-24</date>
+ </refsect2info>
+ <title>
Notes
- </TITLE>
- <PARA>
+ </title>
+ <para>
The <command>SET <replaceable class="parameter">variable</replaceable></command>
statement is a <productname>Postgres</productname> language extension.
</para>
Refer to <command>SHOW</command> and <command>RESET</command> to
display or reset the current values.
</para>
- </REFSECT2>
- </REFSECT1>
+ </refsect2>
+ </refsect1>
- <REFSECT1 ID="R1-SQL-SET-2">
- <TITLE>
+ <refsect1 id="R1-SQL-SET-2">
+ <title>
Usage
- </TITLE>
- <PARA>
- </PARA>
- <ProgramListing>
+ </title>
+ <para>
+ </para>
+ <programlisting>
--Set the style of date to ISO:
--
SET DATESTYLE TO 'ISO';
today
----------------------
1998-03-31 17:41:31+02
- </ProgramListing>
+ </programlisting>
- </REFSECT1>
+ </refsect1>
- <REFSECT1 ID="R1-SQL-SET-3">
- <TITLE>
+ <refsect1 id="R1-SQL-SET-3">
+ <title>
Compatibility
- </TITLE>
- <PARA>
- </PARA>
+ </title>
+ <para>
+ </para>
- <REFSECT2 ID="R2-SQL-SET-4">
- <REFSECT2INFO>
- <DATE>1998-09-24</DATE>
- </REFSECT2INFO>
- <TITLE>
+ <refsect2 id="R2-SQL-SET-4">
+ <refsect2info>
+ <date>1998-09-24</date>
+ </refsect2info>
+ <title>
SQL92
- </TITLE>
- <PARA>
+ </title>
+ <para>
There is no
<command>SET <replaceable class="parameter">variable</replaceable></command>
in <acronym>SQL92</acronym>.
</para>
</refsect2>
</refsect1>
-</REFENTRY>
+</refentry>
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