52.13. pg_constraint
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.)
Note
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.
Note
pg_class.relchecks
needs to agree with the number of check-constraint entries found in this table for each relation.
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