sql 来自哪里的子查询

Question

我正在按照这些思路写一些东西：

select fielda,fieldb,
       (select sum(field1)-sum(field2) as fieldc 
        from tableb 
        where fieldid = list_of_ids[i]) 
from tablea 
where fieldid in (list_of_ids);

在子查询中，我想使用外部 where 子句中的值。因此，如果 list_of_ids 是 123,456,789，子查询中的 fieldid 将是 123，第二个是 456，等等。这可能吗？

Answer 1

您只需要使用 ta.fieldid 而不是 list_of_ids[i]

select ta.fielda,ta.fieldb,
       (select sum(tb.field1)-sum(tb.field2) as fieldc 
        from tableb tb
        where tb.fieldid = ta.fieldid ) 
from tablea  ta
where ta.fieldid in (list_of_ids);

Answer 2

试试这个代码：

select ta.fielda,ta.fieldb,
       (select sum(field1)-sum(field2) as fieldc 
        from tableb tb
        where tb.fieldid = ta.fieldid ) 
from tablea  ta
where ta.fieldid in (list_of_ids);

Answer 3

子查询锚定到外部查询中的单个记录。

select fielda,fieldb,
       (select sum(field1)-sum(field2) as fieldc 
        from tableb 
        where tableb.fieldid = tablea.fieldid) 
from tablea 
where tablea.fieldid in (list_of_ids);

只需使用一个简单的比较运算符将您的子查询与外部查询相关联，您的子查询就会与外部查询找到的任何字段 ID 进行比较。

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