How to list all constraints of a table in PostgreSQL? - 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

Answer 3

I wasn't able to get the above solutions to work. Maybe they're no longer supported or more likely I'm doing something wrong. This is how I got it to work. Note that the "contype" column will be abbreviated with the constraint type (e.g. 'c' for check, 'p' for primary key, etc.). I include that variable in case you want to add a WHERE statement to filter for it after the FROM block.
select pgc.conname as constraint_name,
ccu.table_schema as table_schema,
ccu.table_name,
ccu.column_name,
contype,
pg_get_constraintdef(pgc.oid)
from pg_constraint pgc
join pg_namespace nsp on nsp.oid = pgc.connamespace
join pg_class cls on pgc.conrelid = cls.oid
left join information_schema.constraint_column_usage ccu
on pgc.conname = ccu.constraint_name
and nsp.nspname = ccu.constraint_schema
order by pgc.conname;

Answer 4

SELECT constraint_name, table_name, column_name, ordinal_position FROM information_schema.key_column_usage WHERE table_name = 'put your table name here';