The PostgreSQL 9.0 Reference Manual - Volume 1B

The PostgreSQL 9.0 Reference Manual - Volume 1B - SQL Command Reference
by The PostgreSQL Global Development Group
Paperback (6"x9"), 488 pages
ISBN 9781906966058
RRP £14.95 ($19.95)

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PostgreSQL 9.0 Reference Manual
Volume 1B

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1.130 SET

Name

SET -- change a run-time parameter

Synopsis

SET [ SESSION | LOCAL ] configuration_parameter { TO | = } {
 value | 'value' | DEFAULT }
SET [ SESSION | LOCAL ] TIME ZONE { timezone | LOCAL | DEFAULT }

Description

The SET command changes run-time configuration parameters. Many of the run-time parameters listed in Volume 3: Server Configuration can be changed on-the-fly with SET. (But some require superuser privileges to change, and others cannot be changed after server or session start.) SET only affects the value used by the current session.

If SET (or equivalently SET SESSION) is issued within a transaction that is later aborted, the effects of the SET command disappear when the transaction is rolled back. Once the surrounding transaction is committed, the effects will persist until the end of the session, unless overridden by another SET.

The effects of SET LOCAL last only till the end of the current transaction, whether committed or not. A special case is SET followed by SET LOCAL within a single transaction: the SET LOCAL value will be seen until the end of the transaction, but afterwards (if the transaction is committed) the SET value will take effect.

The effects of SET or SET LOCAL are also canceled by rolling back to a savepoint that is earlier than the command.

If SET LOCAL is used within a function that has a SET option for the same variable (see CREATE FUNCTION), the effects of the SET LOCAL command disappear at function exit; that is, the value in effect when the function was called is restored anyway. This allows SET LOCAL to be used for dynamic or repeated changes of a parameter within a function, while still having the convenience of using the SET option to save and restore the caller's value. However, a regular SET command overrides any surrounding function's SET option; its effects will persist unless rolled back.

Note: In PostgreSQL versions 8.0 through 8.2, the effects of a SET LOCAL would be canceled by releasing an earlier savepoint, or by successful exit from a PL/pgSQL exception block. This behavior has been changed because it was deemed unintuitive.

Parameters

SESSION: Specifies that the command takes effect for the current session. (This is the default if neither SESSION nor LOCAL appears.)
LOCAL: Specifies that the command takes effect for only the current transaction. After COMMIT or ROLLBACK, the session-level setting takes effect again. Note that SET LOCAL will appear to have no effect if it is executed outside a BEGIN block, since the transaction will end immediately.
configuration_parameter: Name of a settable run-time parameter. Available parameters are documented in Volume 3: Server Configuration and below.
value: New value of parameter. Values can be specified as string constants, identifiers, numbers, or comma-separated lists of these, as appropriate for the particular parameter. DEFAULT can be written to specify resetting the parameter to its default value (that is, whatever value it would have had if no SET had been executed in the current session).

Besides the configuration parameters documented in Volume 3: Server Configuration, there are a few that can only be adjusted using the SET command or that have a special syntax:

SCHEMA

SET SCHEMA 'value' is an alias for SET search_path TO value. Only one schema can be specified using this syntax.

NAMES

SET NAMES value is an alias for SET client_encoding TO value.

SEED

Sets the internal seed for the random number generator (the function random). Allowed values are floating-point numbers between -1 and 1, which are then multiplied by 2³¹-1. The seed can also be set by invoking the function setseed:

SELECT setseed(value);

TIME ZONE

SET TIME ZONE value is an alias for SET timezone TO value. The syntax SET TIME ZONE allows special syntax for the time zone specification. Here are examples of valid values:

'PST8PDT': The time zone for Berkeley, California.
'Europe/Rome': The time zone for Italy.
-7: The time zone 7 hours west from UTC (equivalent to PDT). Positive values are east from UTC.
INTERVAL '-08:00' HOUR TO MINUTE: The time zone 8 hours west from UTC (equivalent to PST).
LOCAL
DEFAULT: Set the time zone to your local time zone (that is, the server's default value of timezone; if this has not been explicitly set anywhere, it will be the zone that the server's operating system defaults to).

See Volume 1A: 6.5.3 Time Zones for more information about time zones.

Notes

The function set_config provides equivalent functionality; see Volume 1A: 7.24 System Administration Functions. Also, it is possible to UPDATE the pg_settings system view to perform the equivalent of SET.

Examples

Set the schema search path:

SET search_path TO my_schema, public;

Set the style of date to traditional POSTGRES with “day before month” input convention:

SET datestyle TO postgres, dmy;

Set the time zone for Berkeley, California:

SET TIME ZONE 'PST8PDT';

Set the time zone for Italy:

SET TIME ZONE 'Europe/Rome';

Compatibility

SET TIME ZONE extends syntax defined in the SQL standard. The standard allows only numeric time zone offsets while PostgreSQL allows more flexible time-zone specifications. All other SET features are PostgreSQL extensions.