LEFT-JOIN 代替 oracle (+) with where 子句

Question

上次 post 由于“重复”post（10 年前）而被删除，但我无法根据我的查询调整答案。

我想用 LEFT JOIN 替换 oracle (+)，但我想不通。

FROM a,b,c
WHERE b.a  = '101'
AND a.a    = '202'
AND b.c    = a.c
AND a.d    = c.d(+)
AND ROWNUM = 1;

我试过的是

FROM a
LEFT JOIN c
ON a.d = c.d
WHERE b.a  = '101'
AND a.a    = '202'
AND b.c    = a.c
AND ROWNUM = 1;

但由于我从未从 table b 获取数据，所以它失败了。

Answer 1

您想 INNER JOIN 到 b 然后 LEFT OUTER JOIN 到 c:

FROM  a
      INNER JOIN b
      ON (b.c = a.c)
      LEFT OUTER JOIN c
      ON (a.d = c.d)
WHERE b.a  = '101'
AND   a.a    = '202'
AND   ROWNUM = 1;

您的查询：

FROM a,b,c
WHERE b.a  = '101'
AND a.a    = '202'
AND b.c    = a.c
AND a.d    = c.d(+)
AND ROWNUM = 1;

FROM 子句中的逗号表示 CROSS JOIN.

但是，在 WHERE 子句中您有：

b.c = a.c 将表 a 和 b 之间的连接条件从 CROSS JOIN 更改为 INNER JOIN；和
a.d = c.d(+) 将表 a 和 c 之间的连接条件从 CROSS JOIN 更改为 LEFT OUTER JOIN.

LEFT-JOIN 代替 oracle (+) with where 子句

LEFT-JOIN instead of oracle (+) with where clause

sql

oracle

left-join