How to list all constraints of a table in PostgreSQL?

Question

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

Answer 1

Constraints of the table can be retrieved from catalog-pg-constraint. using the SELECT query.

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}';

and the same can be viewed in PSQL using

\d+ {SCHEMA_NAME.TABLE_NAME}

Answer 2

Here is POSTGRES specific answer ..... it will retrive all columns and their relationship as well

SELECT * FROM (

SELECT
    pgc.contype as constraint_type,
    pgc.conname as constraint_name,
    ccu.table_schema AS table_schema,
    kcu.table_name as table_name,
    CASE WHEN (pgc.contype = 'f') THEN kcu.COLUMN_NAME ELSE ccu.COLUMN_NAME END as column_name, 
    CASE WHEN (pgc.contype = 'f') THEN ccu.TABLE_NAME ELSE (null) END as reference_table,
    CASE WHEN (pgc.contype = 'f') THEN ccu.COLUMN_NAME ELSE (null) END as reference_col,
    CASE WHEN (pgc.contype = 'p') THEN 'yes' ELSE 'no' END as auto_inc,
    CASE WHEN (pgc.contype = 'p') THEN 'NO' ELSE 'YES' END as is_nullable,

        'integer' as data_type,
        '0' as numeric_scale,
        '32' as numeric_precision
FROM
    pg_constraint AS pgc
    JOIN pg_namespace nsp ON nsp.oid = pgc.connamespace
    JOIN pg_class cls ON pgc.conrelid = cls.oid
    JOIN information_schema.key_column_usage kcu ON kcu.constraint_name = pgc.conname
    LEFT JOIN information_schema.constraint_column_usage ccu ON pgc.conname = ccu.CONSTRAINT_NAME 
    AND nsp.nspname = ccu.CONSTRAINT_SCHEMA
 
 UNION
 
    SELECT  null as constraint_type , null as constraint_name , 'public' as "table_schema" ,
    table_name , column_name, null as refrence_table , null as refrence_col , 'no' as auto_inc ,
    is_nullable , data_type, numeric_scale , numeric_precision
    FROM information_schema.columns cols 
    Where 1=1
    AND table_schema = 'public'
    and column_name not in(
        SELECT CASE WHEN (pgc.contype = 'f') THEN kcu.COLUMN_NAME ELSE kcu.COLUMN_NAME END 
        FROM
        pg_constraint AS pgc
        JOIN pg_namespace nsp ON nsp.oid = pgc.connamespace
        JOIN pg_class cls ON pgc.conrelid = cls.oid
        JOIN information_schema.key_column_usage kcu ON kcu.constraint_name = pgc.conname
        LEFT JOIN information_schema.constraint_column_usage ccu ON pgc.conname = ccu.CONSTRAINT_NAME 
        AND nsp.nspname = ccu.CONSTRAINT_SCHEMA
    )
)   as foo

ORDER BY table_name desc