【ORACLE】在结果集字段中只有一列要使用组函数MAX，使用GROUP BY效率并不是最高的。

原SQL如下，效率低的让人不能忍受，然后就在想有没有其它变通的方式：

SELECT MAX(C.INVDATE), D.HAIER_YEAR, D.HAIER_SWEEK_TO_YEAR, C.GOODS_ID FROM ECC_OMS.V_TJ_STOCK C, ECC_OMS.DATE_WEEK_YEAR D WHERE C.INVDATE = D.SDATE GROUP BY D.HAIER_YEAR, D.HAIER_SWEEK_TO_YEAR, C.GOODS_ID

执行计划如下：

SELECT STATEMENT, GOAL = ALL_ROWS 13641 651105 21486465

HASH GROUP BY 13641 651105 21486465

HASH JOIN 6580 1026081 33860673

TABLE ACCESS FULL ECC_OMS DATE_WEEK_YEAR 5 2397 35955

TABLE ACCESS FULL ECC_OMS V_TJ_STOCK 6563 1026081 18469458

想了一会，试着用ORDER BY DESC和ROWNUM=1变通一下：

SELECT C.INVDATE, D.HAIER_YEAR, D.HAIER_SWEEK_TO_YEAR, C.GOODS_ID FROM ECC_OMS.V_TJ_STOCK C, ECC_OMS.DATE_WEEK_YEAR D WHERE C.INVDATE = D.SDATE AND ROWNUM = 1 ORDER BY C.INVDATE DESC

执行计划如下：

SELECT STATEMENT, GOAL = ALL_ROWS 3 1 33

COUNT STOPKEY

NESTED LOOPS 3 1 33

TABLE ACCESS BY INDEX ROWID ECC_OMS V_TJ_STOCK 2 1026081 18469458

INDEX FULL SCAN DESCENDING ECC_OMS V_TJ_STOCK_IDX01 2 1

TABLE ACCESS BY INDEX ROWID ECC_OMS DATE_WEEK_YEAR 1 1 15

INDEX UNIQUE SCAN ECC_OMS DATE_WEEK_YEAR 1 1

请各位大侠指教。