Cómo ver restricciones en PostgreSQL
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>';
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