psql-drop-create-constraints.sql

SELECT 'ALTER TABLE '||nspname||'.'||relname||' ADD CONSTRAINT '||conname||' '|| pg_get_constraintdef(pg_constraint.oid)||';'
FROM pg_constraint 
INNER JOIN pg_class ON conrelid=pg_class.oid 
INNER JOIN pg_namespace ON pg_namespace.oid=pg_class.relnamespace 
ORDER BY CASE WHEN contype='f' THEN 0 ELSE 1 END DESC,contype DESC,nspname DESC,relname DESC,conname DESC;

SELECT 'ALTER TABLE '||nspname||'.'||relname||' DROP CONSTRAINT '||conname||';'
FROM pg_constraint 
INNER JOIN pg_class ON conrelid=pg_class.oid 
INNER JOIN pg_namespace ON pg_namespace.oid=pg_class.relnamespace 
ORDER BY CASE WHEN contype='f' THEN 0 ELSE 1 END,contype,nspname,relname,conname;