llaves_externas
'
            SELECT
                TBL.relname AS FORANEA,
                VEX.attname AS CONTRAPARTE,
                VAR.attname AS VARIABLE
            FROM pg_constraint AS CNST
            LEFT JOIN pg_class AS TBL ON CNST.conrelid = TBL.oid
            LEFT JOIN pg_attribute AS VAR
                ON (CNST.conkey[1]=VAR.attnum AND TBL.oid=VAR.attrelid)
            LEFT JOIN pg_class AS FRN
                ON CNST.confrelid=FRN.oid
            LEFT JOIN pg_attribute AS VEX
            ON (CNST.confkey[1]=VEX.attnum AND FRN.oid=VEX.attrelid)
            WHERE FRN.relname='pg_ts_config'
            AND TBL.relname IS NOT NULL;'