information_schema.table_constraints lists names of constraints (primary keys, foreign keys, unique values and checks) that are associated with a table.
select * from information_schema.table_constraints where table_name = 'tabXYZ' and constraint_type = 'PRIMARY KEY';
select * from information_schema.table_constraints where table_name = 'tabXYZ' and constraint_type = 'FOREIGN KEY';
select * from information_schema.table_constraints where table_name = 'tabXYZ' and constraint_type = 'UNIQUE';
select * from information_schema.table_constraints where table_name = 'tabXYZ' and constraint_type = 'CHECK';