primary_key

# File activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb, line 399
        def primary_key(table)
          pks = exec_query(            SELECT attr.attname            FROM pg_attribute attr            INNER JOIN pg_constraint cons ON attr.attrelid = cons.conrelid AND attr.attnum = any(cons.conkey)            WHERE cons.contype = 'p'              AND cons.conrelid = '#{quote_table_name(table)}'::regclass, 'SCHEMA').rows
          return nil unless pks.count == 1
          pks[0][0]
        end