SET CONSTRAINTS(7) PostgreSQL 9.4.15 Documentation SET CONSTRAINTS(7)
NAME
SET_CONSTRAINTS - set constraint check timing for the current
transaction
SYNOPSIS
SET CONSTRAINTS { ALL | name [, ...] } { DEFERRED | IMMEDIATE }
DESCRIPTION
SET CONSTRAINTS sets the behavior of constraint checking within the
current transaction. IMMEDIATE constraints are checked at the end of
each statement. DEFERRED constraints are not checked until transaction
commit. Each constraint has its own IMMEDIATE or DEFERRED mode.
Upon creation, a constraint is given one of three characteristics:
DEFERRABLE INITIALLY DEFERRED, DEFERRABLE INITIALLY IMMEDIATE, or NOT
DEFERRABLE. The third class is always IMMEDIATE and is not affected by
the SET CONSTRAINTS command. The first two classes start every
transaction in the indicated mode, but their behavior can be changed
within a transaction by SET CONSTRAINTS.
SET CONSTRAINTS with a list of constraint names changes the mode of
just those constraints (which must all be deferrable). Each constraint
name can be schema-qualified. The current schema search path is used to
find the first matching name if no schema name is specified. SET
CONSTRAINTS ALL changes the mode of all deferrable constraints.
When SET CONSTRAINTS changes the mode of a constraint from DEFERRED to
IMMEDIATE, the new mode takes effect retroactively: any outstanding
data modifications that would have been checked at the end of the
transaction are instead checked during the execution of the SET
CONSTRAINTS command. If any such constraint is violated, the SET
CONSTRAINTS fails (and does not change the constraint mode). Thus, SET
CONSTRAINTS can be used to force checking of constraints to occur at a
specific point in a transaction.
Currently, only UNIQUE, PRIMARY KEY, REFERENCES (foreign key), and
EXCLUDE constraints are affected by this setting. NOT NULL and CHECK
constraints are always checked immediately when a row is inserted or
modified (not at the end of the statement). Uniqueness and exclusion
constraints that have not been declared DEFERRABLE are also checked
immediately.
The firing of triggers that are declared as "constraint triggers" is
also controlled by this setting -- they fire at the same time that the
associated constraint should be checked.
NOTES
Because PostgreSQL does not require constraint names to be unique
within a schema (but only per-table), it is possible that there is more
than one match for a specified constraint name. In this case SET
CONSTRAINTS will act on all matches. For a non-schema-qualified name,
once a match or matches have been found in some schema in the search
path, schemas appearing later in the path are not searched.
This command only alters the behavior of constraints within the current
transaction. Issuing this outside of a transaction block emits a
warning and otherwise has no effect.
COMPATIBILITY
This command complies with the behavior defined in the SQL standard,
except for the limitation that, in PostgreSQL, it does not apply to NOT
NULL and CHECK constraints. Also, PostgreSQL checks non-deferrable
uniqueness constraints immediately, not at end of statement as the
standard would suggest.
PostgreSQL 9.4.15 2017 SET CONSTRAINTS(7)
PostgreSQL 9.4.15 - Generated Tue Nov 28 15:28:57 CST 2017