SET — change a run-time parameter
SET [ SESSION | LOCAL ]configuration_parameter
{ TO | = } {value
| 'value
' | DEFAULT } SET [ SESSION | LOCAL ] TIME ZONE {timezone
| LOCAL | DEFAULT }
The SET
command changes run-time configuration
parameters. Many of the run-time parameters listed in
Chapter 17 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.
In LightDB 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.
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. Issuing this
outside of a transaction block emits a warning and otherwise has
no effect.
configuration_parameter
Name of a settable run-time parameter. Available parameters are documented in Chapter 17 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 Chapter 17, there are a few that can only be
adjusted using the SET
command or that have a
special syntax:
SCHEMA
SET SCHEMA '
is an alias for
value
'SET search_path TO
. Only one
schema can be specified using this syntax.
value
NAMES
SET NAMES
is an alias for
value
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
is an alias
for value
SET timezone TO
. The
syntax value
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
).
Timezone settings given as numbers or intervals are internally
translated to POSIX timezone syntax. For example, after
SET TIME ZONE -7
, SHOW TIME ZONE
would
report <-07>+07
.
See Section 8.5.3 for more information about time zones.
The function set_config
provides equivalent
functionality; see Section 9.27.1.
Also, it is possible to UPDATE the
pg_settings
system view to perform the equivalent of SET
.
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';
SET TIME ZONE
extends syntax defined in the SQL
standard. The standard allows only numeric time zone offsets while
LightDB allows more flexible
time-zone specifications. All other SET
features are LightDB extensions.