The catalog pg_constraint stores check, primary key, unique, foreign key, and exclusion constraints on tables. (Column constraints are not treated specially. Every column constraint is equivalent to some table constraint.) Not-null constraints are represented in the pg_attribute catalog, not here.
User-defined constraint triggers (created with CREATE CONSTRAINT TRIGGER) also give rise to an entry in this table.
Check constraints on domains are stored here, too.
Table 51.13. pg_constraint Columns
In the case of an exclusion constraint, conkey is only useful for constraint elements that are simple column references. For other cases, a zero appears in conkey and the associated index must be consulted to discover the expression that is constrained. (conkey thus has the same contents as pg_index.indkey for the index.)
consrc is not updated when referenced objects change; for example, it won't track renaming of columns. Rather than relying on this field, it's best to use pg_get_constraintdef() to extract the definition of a check constraint.
pg_class.relchecks needs to agree with the number of check-constraint entries found in this table for each relation.
Name
Type
References
Description
oid
oid
Row identifier (hidden attribute; must be explicitly selected)
conname
name
Constraint name (not necessarily unique!)
connamespace
oid
pg_namespace.oid
The OID of the namespace that contains this constraint
contype
char
c = check constraint, f = foreign key constraint, p = primary key constraint, u = unique constraint, t = constraint trigger, x = exclusion constraint
condeferrable
bool
Is the constraint deferrable?
condeferred
bool
Is the constraint deferred by default?
convalidated
bool
Has the constraint been validated? Currently, can only be false for foreign keys and CHECK constraints
conrelid
oid
pg_class.oid
The table this constraint is on; 0 if not a table constraint
contypid
oid
pg_type.oid
The domain this constraint is on; 0 if not a domain constraint
conindid
oid
pg_class.oid
The index supporting this constraint, if it's a unique, primary key, foreign key, or exclusion constraint; else 0
confrelid
oid
pg_class.oid
If a foreign key, the referenced table; else 0
confupdtype
char
Foreign key update action code: a = no action, r = restrict, c = cascade, n = set null, d = set default
confdeltype
char
Foreign key deletion action code: a = no action, r = restrict, c = cascade, n = set null, d = set default
confmatchtype
char
Foreign key match type: f = full, p = partial, s = simple
conislocal
bool
This constraint is defined locally for the relation. Note that a constraint can be locally defined and inherited simultaneously.
coninhcount
int4
The number of direct inheritance ancestors this constraint has. A constraint with a nonzero number of ancestors cannot be dropped nor renamed.
connoinherit
bool
This constraint is defined locally for the relation. It is a non-inheritable constraint.
conkey
int2[]
pg_attribute.attnum
If a table constraint (including foreign keys, but not constraint triggers), list of the constrained columns
confkey
int2[]
pg_attribute.attnum
If a foreign key, list of the referenced columns
conpfeqop
oid[]
pg_operator.oid
If a foreign key, list of the equality operators for PK = FK comparisons
conppeqop
oid[]
pg_operator.oid
If a foreign key, list of the equality operators for PK = PK comparisons
conffeqop
oid[]
pg_operator.oid
If a foreign key, list of the equality operators for FK = FK comparisons
conexclop
oid[]
pg_operator.oid
If an exclusion constraint, list of the per-column exclusion operators
conbin
pg_node_tree
If a check constraint, an internal representation of the expression
consrc
text
If a check constraint, a human-readable representation of the expression