set.sgml

<REFENTRY ID="SQL-SET">
 <REFMETA>
  <REFENTRYTITLE>
   SET
  </REFENTRYTITLE>
  <REFMISCINFO>SQL - Language Statements</REFMISCINFO>
 </REFMETA>
 <REFNAMEDIV>
  <REFNAME>
   SET
  </REFNAME>
  <REFPURPOSE>
   Set run-time parameters for session
  </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>

  <REFSECT2 ID="R2-SQL-SET-1">
   <REFSECT2INFO>
    <DATE>1998-09-24</DATE>
   </REFSECT2INFO>
   <TITLE>
    Inputs
   </TITLE>
   <PARA>
		
    <VARIABLELIST>
     <VARLISTENTRY>
      <TERM>
       <REPLACEABLE CLASS="PARAMETER">variable</REPLACEABLE>
      </TERM>
      <LISTITEM>
       <para>
	Settable global parameter.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term>
       <REPLACEABLE CLASS="PARAMETER">value</REPLACEABLE>
      </term>
      <listitem>
       <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>
	   ISO
	  </TERM>
	  <LISTITEM>
	   <PARA>
	    use ISO 8601-style dates and times
	   </para>
	  </listitem>
	 </varlistentry>
	 <VARLISTENTRY>
	  <TERM>
	   SQL
	  </TERM>
	  <LISTITEM>
	   <PARA>
	    use Oracle/Ingres-style dates and times
	   </para>
	  </listitem>
	 </varlistentry>
	 <VARLISTENTRY>
	  <TERM>
	   Postgres
	  </TERM>
	  <LISTITEM>
	   <PARA>
	    use traditional <productname>Postgres</productname> format
	   </para>
	  </listitem>
	 </varlistentry>
	 <VARLISTENTRY>
	  <TERM>
	   European
	  </TERM>
	  <LISTITEM>
	   <PARA>
	    use dd/mm/yyyy for numeric date representations.
	   </para>
	  </listitem>
	 </varlistentry>
	 <VARLISTENTRY>
	  <TERM>
	   NonEuropean
	  </TERM>
	  <LISTITEM>
	   <PARA>
	    use mm/dd/yyyy for numeric date representations.
	   </para>
	  </listitem>
	 </varlistentry>
	 <VARLISTENTRY>
	  <TERM>
	   German
	  </TERM>
	  <LISTITEM>
	   <PARA>
	    use dd.mm.yyyy for numeric date representations.
	   </para>
	  </listitem>
	 </varlistentry>
	 <VARLISTENTRY>
	  <TERM>
	   US
	  </TERM>
	  <LISTITEM>
	   <PARA>
	    same as 'NonEuropean'
	   </para>
	  </listitem>
	 </varlistentry>
	 <VARLISTENTRY>
	  <TERM>
	   default
	  </TERM>
	  <LISTITEM>
	   <PARA>
	    restores the default values ('US,Postgres')
	   </para>
	  </listitem>
	 </varlistentry>
	</variablelist>
       </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
      </term>
      <listitem>
       <para>
	The possible values for timezone depends on your operating
	system. For example on Linux /usr/lib/zoneinfo contains the
	database of timezones.
       </para>
       <para>
	Here are some valid values for timezone:
				
	<variablelist>
	 <varlistentry>
	  <term>
	   'PST8PDT'
	  </term>
	  <listitem>
	   <para>
	    set the timezone for California
	   </para>
	  </listitem>
	 </varlistentry>
	 <varlistentry>
	  <term>
	   'Portugal'
	  </term>
	  <listitem>
	   <para>
	    set time zone for Portugal.
	   </para>
	  </listitem>
	 </varlistentry>
	 <varlistentry>
	  <term>
	   'Europe/Rome'
	  </term>
	  <listitem>
	   <para>
	    set time zone for Italy.
	   </para>
	  </listitem>
	 </varlistentry>
	 <varlistentry>
	  <term>
	   DEFAULT
	  </term>
	  <listitem>
	   <para>
	    set time zone to your local timezone
	    (value of the TZ environment variable).
	   </para>
	  </listitem>
	 </varlistentry>
	</variablelist>
       </para>
       <para>
	If an invalid time zone is specified, the time zone
	becomes GMT (on most systems anyway).
       </para>
       <para>
	A frontend which uses libpq may be initialized by setting the PGTZ
	environment variable.
       </para>
       <para>
	The second syntax shown above, allows one to set the timezone
	with a syntax similar to SQL92 <command>SET TIME ZONE</command>.
	The LOCAL keyword is just an alternate form
	of DEFAULT for SQL92 compatibility.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
   <para>
    There are also several internal or optimization
    parameters which can be specified
    by the <command>SET</command> command:
    
    <variablelist>
     <varlistentry>
      <term>
       COST_HEAP
      </term>
      <listitem>
       <para>
	Sets the default cost of a heap scan for use by the optimizer.
	
	<variablelist>
	 <varlistentry>
	  <term>
	   <replaceable class="parameter">float4</replaceable>
	  </term>
	  <listitem>
	   <para>
	    Set the cost of a heap scan to the specified floating point value.
	   </para>
	  </listitem>
	 </varlistentry>
	 
	 <varlistentry>
	  <term>
	   DEFAULT
	  </term>
	  <listitem>
	   <para>
	    Sets the cost of a heap scan to the default value.
	   </para>
	  </listitem>
	 </varlistentry>
	</variablelist>
       </para>
       <para>
	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
      </term>
      <listitem>
       <para>
	Sets the number of rows returned by a query.
       </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.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>

    <variablelist>
     <varlistentry>
      <term>
       TRANSACTION ISOLATION LEVEL
      </term>
      <listitem>
       <para>
	Sets the isolation level for the current transaction.
	
	<variablelist>
	 <varlistentry>
	  <term>
	   <replaceable class="parameter">value</replaceable>
	  </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.
	   </para>
	  </listitem>
	 </varlistentry>
   </para>
	 
	 <varlistentry>
	  <term>
	   DEFAULT
	  </term>
	  <listitem>
	   <para>
		Sets the isolation level for the current transaction to
		'READ COMMITTED'.
	   </para>
	  </listitem>
	 </varlistentry>
	</variablelist>
       </para>

    <variablelist>
     <varlistentry>
      <term>
       CLIENT_ENCODING | NAMES
      </term>
      <listitem>
       <para>
	Sets the multi-byte client encoding
	
	<variablelist>
	 <varlistentry>
	  <term>
	   <replaceable class="parameter">value</replaceable>
	  </term>
	  <listitem>
	   <para>
		Sets the multi-byte client encoding.
	   </para>
	  </listitem>
	 </varlistentry>
   </para>
	 
	 <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>

    <variablelist>
     <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>
   </para>
	 
	 <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>



  </REFSECT2>
  
  <REFSECT2 ID="R2-SQL-SET-2">
   <REFSECT2INFO>
    <DATE>1998-09-24</DATE>
   </REFSECT2INFO>
   <TITLE>
    Outputs
   </TITLE>
   <PARA>
    
    <VARIABLELIST>
     <VARLISTENTRY>
      <TERM>
       <returnvalue>SET VARIABLE</returnvalue>
      </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.
       </para>
      </listitem>
     </varlistentry>
     
    </VARIABLELIST>
   </para>
  </REFSECT2>
 </REFSYNOPSISDIV>
 
 <REFSECT1 ID="R1-SQL-SET-1">
  <REFSECT1INFO>
   <DATE>1998-09-24</DATE>
  </REFSECT1INFO>
  <TITLE>
   Description
  </TITLE>
  <PARA>
   <command>SET</command> will modify configuration parameters for variable during
   a session.
  </para>
  <para>
   Current values can be obtained using <command>SHOW</command>, and values
   can be restored to the defaults using <command>RESET</command>.
   Parameters and values are case-insensitive. Note that the value
   field is always specified as a string, so is enclosed in
   single-quotes.
  </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
   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>
    Notes
   </TITLE>
   <PARA>
    The <command>SET <replaceable class="parameter">variable</replaceable></command>
    statement is a <productname>Postgres</productname> language extension.
   </para>
   <para>
    Refer to <command>SHOW</command> and <command>RESET</command> to 
    display or reset the current values.
   </para>
  </REFSECT2>
 </REFSECT1>
 
 <REFSECT1 ID="R1-SQL-SET-2">
  <TITLE>
   Usage
  </TITLE>
  <PARA>
  </PARA>
  <ProgramListing>
   --Set the style of date to ISO:
   --
   SET DATESTYLE TO 'ISO';
  </programlisting>
  <programlisting> 
   --Enable GEQO for queries with 4 or more tables
   --
   SET GEQO ON=4;
  </programlisting>
  <programlisting> 
   --Set GEQO to default:
   --
   SET GEQO = DEFAULT;
  </programlisting>
  <programlisting> 
   --set the timezone for Berkeley, California:
   SET TIME ZONE 'PST8PDT';
   
   SELECT CURRENT_TIMESTAMP AS today;
   
   today
   ----------------------
   1998-03-31 07:41:21-08
  </programlisting>
  <programlisting> 
   --set the timezone for Italy:
   SET TIME ZONE 'Europe/Rome';
   
   SELECT CURRENT_TIMESTAMP AS today;
   
   today
   ----------------------
   1998-03-31 17:41:31+02
  </ProgramListing>
  
 </REFSECT1>

 <REFSECT1 ID="R1-SQL-SET-3">
  <TITLE>
   Compatibility
  </TITLE>
  <PARA>
  </PARA>
  
  <REFSECT2 ID="R2-SQL-SET-4">
   <REFSECT2INFO>
    <DATE>1998-09-24</DATE>
   </REFSECT2INFO>
   <TITLE>
    SQL92
   </TITLE>
   <PARA>
    There is no
    <command>SET <replaceable class="parameter">variable</replaceable></command>
    in <acronym>SQL92</acronym>.
    
    The <acronym>SQL92</acronym> syntax for <command>SET TIME ZONE</command>
    is slightly different,
    allowing only a single integer value for time zone specification:
    
    <programlisting>
     SET TIME ZONE { interval_value_expression | LOCAL }
    </programlisting>
   </para>
  </refsect2>
 </refsect1>
</REFENTRY>

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