# File lib/active_record/connection_adapters/postgresql_adapter.rb, line 851 def primary_key(table) row = exec_query("SELECT DISTINCT(attr.attname)\nFROM pg_attribute attr\nINNER JOIN pg_depend dep ON attr.attrelid = dep.refobjid AND attr.attnum = dep.refobjsubid\nINNER JOIN pg_constraint cons ON attr.attrelid = cons.conrelid AND attr.attnum = cons.conkey[1]\nWHERE cons.contype = 'p'\nAND dep.refobjid = $1::regclass\n", 'SCHEMA', [[nil, table]]).rows.first row && row.first end