pk_and_sequence_for

# File activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb, line 740
      def pk_and_sequence_for(table) #:nodoc:
        # First try looking for a sequence with a dependency on the
        # given table's primary key.
        result = query("SELECT attr.attname, seq.relname\nFROM pg_class      seq,\npg_attribute  attr,\npg_depend     dep,\npg_namespace  name,\npg_constraint cons\nWHERE seq.oid           = dep.objid\nAND seq.relkind       = 'S'\nAND attr.attrelid     = dep.refobjid\nAND attr.attnum       = dep.refobjsubid\nAND attr.attrelid     = cons.conrelid\nAND attr.attnum       = cons.conkey[1]\nAND cons.contype      = 'p'\nAND dep.refobjid      = '\#{quote_table_name(table)}'::regclass\n", 'PK and serial sequence')[0]

        if result.nil? or result.empty?
          # If that fails, try parsing the primary key's default value.
          # Support the 7.x and 8.0 nextval('foo'::text) as well as
          # the 8.1+ nextval('foo'::regclass).
          result = query("SELECT attr.attname,\nCASE\nWHEN split_part(def.adsrc, '''', 2) ~ '.' THEN\nsubstr(split_part(def.adsrc, '''', 2),\nstrpos(split_part(def.adsrc, '''', 2), '.')+1)\nELSE split_part(def.adsrc, '''', 2)\nEND\nFROM pg_class       t\nJOIN pg_attribute   attr ON (t.oid = attrelid)\nJOIN pg_attrdef     def  ON (adrelid = attrelid AND adnum = attnum)\nJOIN pg_constraint  cons ON (conrelid = adrelid AND adnum = conkey[1])\nWHERE t.oid = '\#{quote_table_name(table)}'::regclass\nAND cons.contype = 'p'\nAND def.adsrc ~* 'nextval'\n", 'PK and custom sequence')[0]
        end

        # [primary_key, sequence]
        [result.first, result.last]
      rescue
        nil
      end