1998-09-01 17:53:09 +02:00
<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>
1998-12-29 03:24:47 +01:00
</refnamediv>
1998-09-01 17:53:09 +02:00
<REFSYNOPSISDIV>
<REFSYNOPSISDIVINFO>
1998-09-25 15:42:46 +02:00
<DATE>1998-09-24</DATE>
1998-09-01 17:53:09 +02:00
</REFSYNOPSISDIVINFO>
<SYNOPSIS>
<REPLACEABLE CLASS="PARAMETER">
</REPLACEABLE>
SET <REPLACEABLE CLASS="PARAMETER">variable</REPLACEABLE> { TO | = } { '<REPLACEABLE CLASS="PARAMETER">value</REPLACEABLE>' | DEFAULT }
SET TIME ZONE { '<REPLACEABLE CLASS="PARAMETER">timezone</REPLACEABLE>' | LOCAL };
</SYNOPSIS>
1998-12-29 03:24:47 +01:00
<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:
<programlisting>
bool EuroDates = false
true
int DateStyle = USE_ISO_DATES
USE_POSTGRES_DATES
USE_ISO_DATES
USE_SQL_DATES
USE_GERMAN_DATES
</programlisting>
</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
1999-02-02 04:45:56 +01:00
for statements with 6 or more tables.
1998-12-29 03:24:47 +01:00
</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
1999-03-07 13:00:40 +01:00
statements of eleven or more tables.
1998-12-29 03:24:47 +01:00
(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.
1999-02-18 07:01:11 +01:00
1998-12-29 03:24:47 +01:00
<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>
1999-02-18 07:01:11 +01:00
The frontend may be initialized by setting the PGKSQO
1998-12-29 03:24:47 +01:00
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>
</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
1998-09-01 17:53:09 +02:00
a session.
1998-12-29 03:24:47 +01:00
</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>
1999-02-02 21:30:18 +01:00
<programlisting>
1999-02-14 05:57:02 +01:00
--Enable GEQO for queries with 4 or more tables
1999-02-02 21:30:18 +01:00
--
SET GEQO ON=4;
</programlisting>
1998-12-29 03:24:47 +01:00
<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>
1998-09-01 17:53:09 +02:00
</REFENTRY>
