我具有以下表结构：
Table A (A1, ...) where A1 is PK
Table B (B1, B2, ...) where A.A1 = B.B1 and B2 is PK
Table C (C1, C2, C3, ...) where C.C1 = B.B2 and C1 is PK
给定提供了A.A1和C.C2，我需要获得C3的MAX（）。以下显然不起作用：
select c.c3
from A a join B b on a.A1 = b.B1
join C c on b.B2 = c.C1
where a.A1 = '123'
and c.C2 = to_date('01-01-2000', 'mm-dd-yyyy')
and c.C3 = (
select max(c3)
from C
where c1 = c.C1)
查询不返回任何内容。但是，当我尝试：
select max(c.c3)
from A a join B b on a.A1 = b.B1
join C c on b.B2 = c.C1
group by a.A1, c.C2
having a.A1 = '123'
and c.C2 = to_date('01-01-2000', 'mm-dd-yyyy')
似乎返回正确的值，但是速度很慢。有没有办法让它与第一个查询一起使用（不分区）？
您可以尝试WITH子句。
您的查询可能是这样的：
;WITH C AS(
select c.c3
from A a join B b on a.A1 = b.B1
join C c on b.B2 = c.C1
where a.A1 = '123'
and c.C2 = to_date('01-01-2000', 'mm-dd-yyyy')
)
SELECT MAX(C3) FROM C
或者简单地说，
select max(cs)
from (
select c.c3 as cs
from A a join B b on a.A1 = b.B1
join C c on b.B2 = c.C1
where a.A1 = '123'
and c.C2 = to_date('01-01-2000', 'mm-dd-yyyy')
)
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