Oracle 外连接答案

【问题标题】：Oracle outer joinsOracle 外连接
【发布时间】：2019-08-30 08:29:18
【问题描述】：

当我从表 a 运行时返回两条记录。

从 a.id = '123' 中选择 *

然后我创建了一个临时表 t6，注意：在这个临时表中没有返回 a.id 123 的记录。我使用 where 子句 a.id 123 对表 a 和 t6 进行了左连接，并期望返回 2 条记录，其中表 t6 中的值将为空或空白。但它没有返回任何行。我想知道如何修复以使其正常工作。

select a.*, t6.*
from 
(select t5.column1, t5.column2, t1.column3, t1.column9, t2.column9, t3.column9, t4.column9
from            (select column3, column8, column9 from t7
                where upper(column8) = upper('abcd')
                )  t1
                join (select column3, column8, column9 from t7               
                where upper(column8) = upper('efgh')
                ) t2
                on t2.column3 = t1.column3
                and t1.column3 in (select id2 from a where a.id = '123')
                left outer join
                (select column3, column8, column9 from t7
                where upper(column8) = upper('ijkl')
                ) t3
                on t3.column3 = t1.column3    
                left outer join
               (select column3, column8, column9 from t7
                where upper(column8) = upper('mnop')
                ) t4
                on t4.column3 = t1.column3
                join t5  
                on t1.column9 =  t5.column10
) t6
left join
a
on a.id2 = t6.column3
where a.id = '123'

【问题讨论】：

如果您给我们测试数据和预期结果示例，希望有人可以帮助您。

标签： sql oracle outer-join

【解决方案1】：

表 A 应位于左侧，#t6 应位于右侧。

from a 
left join #t6 on on a.id2 = t6.column3

查询

select a.*, t6.*
from a
left join
(select t5.column1, t5.column2, t1.column3, t1.column9, t2.column9, t3.column9, t4.column9
from            (select column3, column8, column9 from t7
                where upper(column8) = upper('abcd')
                )  t1
                join (select column3, column8, column9 from t7               
                where upper(column8) = upper('efgh')
                ) t2
                on t2.column3 = t1.column3
                and t1.column3 in (select id2 from a where a.id = '123')
                left outer join
                (select column3, column8, column9 from t7
                where upper(column8) = upper('ijkl')
                ) t3
                on t3.column3 = t1.column3    
                left outer join
               (select column3, column8, column9 from t7
                where upper(column8) = upper('mnop')
                ) t4
                on t4.column3 = t1.column3
                join t5  
                on t1.column9 =  t5.column10
) t6

on a.id2 = t6.column3
where a.id = '123'

【讨论】：

【解决方案2】：

将您的 LEFT JOIN 更改为 RIGHT JOIN。

或者改变JOIN链的方向：

SELECT a.*, t6.*
FROM a LEFT JOIN ( SELECT ..... ) ON a.id2 = t6.column3
WHERE a.id = '123'

【讨论】：

【解决方案3】：

如果我理解主表是 a，那么你必须在第一个位置写表 a，如下所示：

select a.*, t6.*
from a left join
(select t5.column1, t5.column2, t1.column3, t1.column9, t2.column9, t3.column9, t4.column9
from            (select column3, column8, column9 from t7
                where upper(column8) = upper('abcd')
                )  t1
                join (select column3, column8, column9 from t7               
                where upper(column8) = upper('efgh')
                ) t2
                on t2.column3 = t1.column3
                and t1.column3 in (select id2 from a where a.id = '123')
                left outer join
                (select column3, column8, column9 from t7
                where upper(column8) = upper('ijkl')
                ) t3
                on t3.column3 = t1.column3    
                left outer join
               (select column3, column8, column9 from t7
                where upper(column8) = upper('mnop')
                ) t4
                on t4.column3 = t1.column3
                join t5  
                on t1.column9 =  t5.column10
) t6
on a.id2 = t6.column3
where a.id = '123'

【讨论】：