Oracle两表联合查询group by的sum后，显示max，竟然花了1.6秒，请教如何优化。 数据也就20000行而已

尽量减少查询结果集，连接查询的结果 SELECT C.CLIENTNO,C.CNAME,QUERY1.TAMOUNT FROM CLIENT C,(SELECT CLIENTNO,SUM(AMOUNT) TAMOUNT FROM PURCHASE GROUP BY CLIENTNO order by TAMMOUNT desc) QUERY1 WHERE C.CLIENTNO = QUERY1.CLIENTNO and Query1.ROWNUM=1