1、使用left join時從表的過濾

WITH a AS( SELECT 'A' aid FROM dual UNION ALL SELECT 'B' FROM dual UNION ALL SELECT 'C' FROM dual UNION ALL SELECT 'D' FROM dual UNION ALL SELECT 'E' FROM dual ), b AS( SELECT 'A' aid,10 num,1 type FROM dual UNION ALL SELECT 'B',20,2 FROM dual UNION ALL SELECT 'D',30,1 FROM dual UNION ALL SELECT 'E',10 ,1 FROM dual ) SELECT t1.aid,NVL(t2.num,0) num,'0通過WHERE過濾' 備注 FROM a t1 LEFT JOIN b t2 ON t2.aid = t1.aid WHERE t2.type = 1 UNION ALL SELECT t1.aid,NVL(t2.num,0),'1通過JOIN條件過濾' FROM a t1 LEFT JOIN b t2 ON t2.aid = t1.aid AND t2.type = 1 ORDER BY 3,1,2

結果如下：

2、使用（+）外連接時過濾從表

WITH a AS( SELECT 'A' aid FROM dual UNION ALL SELECT 'B' FROM dual UNION ALL SELECT 'C' FROM dual UNION ALL SELECT 'D' FROM dual UNION ALL SELECT 'E' FROM dual ), b AS( SELECT 'A' aid,10 num,1 type FROM dual UNION ALL SELECT 'B',20,2 FROM dual UNION ALL SELECT 'D',30,1 FROM dual UNION ALL SELECT 'E',10 ,1 FROM dual ) SELECT t1.aid,NVL(t2.num,0) num,'0不用外連接標識過濾'備注 FROM a t1,b t2 WHERE t2.aid(+) = t1.aid AND t2.type = 1 UNION ALL SELECT t1.aid,NVL(t2.num,0),'1使用外連接標識過濾' FROM a t1,b t2 WHERE t2.aid(+) = t1.aid AND t2.type(+) = 1 ORDER BY 3,1,2

結果如下

總結

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