How to list all constraints (Primary key, check, unique mutual exclusive, ..) of a table in PostgreSQL?


Constraints can be retrieved via pg_catalog.pg_constraint.

SELECT con.*
       FROM pg_catalog.pg_constraint con
            INNER JOIN pg_catalog.pg_class rel
                       ON rel.oid = con.conrelid
            INNER JOIN pg_catalog.pg_namespace nsp
                       ON nsp.oid = connamespace
       WHERE nsp.nspname = '<schema name>'
             AND rel.relname = '<table name>';

Replace <schema name> with the name of your schema and <table name> with the name of your table.

  • 4
    Notice that pg_catalog.pg_constraint does not contain NOT NULL constraints. – Luís de Sousa Jul 24 '19 at 8:30

In the psql command line this information is in the table sheet, obtained with the \d+ command. d+ also informs on the NOT NULL constraints, something that is not present in the pg_catalog.pg_constraint table. An example:

# \d+ observations.stream   
                                                  Table "observations.stream"
 Column |       Type        | Collation | Nullable | Default | Storage  | Stats target |                 Description                 
 id     | integer           |           | not null |         | plain    |              | 
 name   | character varying |           | not null |         | extended |              | This should be a table in the import schema
 min_id | integer           |           | not null |         | plain    |              | 
 about  | character varying |           | not null |         | extended |              | 
    "stream_pkey" PRIMARY KEY, btree (id)
    "stream_name_key" UNIQUE CONSTRAINT, btree (name)
Check constraints:
    "stream_id_check" CHECK (id > 0)
Referenced by:
    TABLE "profile" CONSTRAINT "profile_id_stream_fkey" FOREIGN KEY (id_stream) REFERENCES stream(id)

The caveat here is that you do not get the names of all the constraints this way.

  • I see constraint names in your posted output. – ypercubeᵀᴹ Jul 24 '19 at 8:35

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