在Oracle SQL中查找列的最大值
我有以下表格结构:在Oracle SQL中查找列的最大值,sql,oracle,aggregate-functions,Sql,Oracle,Aggregate Functions,我有以下表格结构: 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 如果提供了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
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
如果提供了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,当我尝试时:
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')
它似乎返回了正确的值,但速度很慢。有没有办法让它处理第一个查询(无分区)?您可以尝试使用
with
子句
您的查询可以是这样的:
;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')
)
为什么不在选择中使用max(c3)
select max(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 = date '2000-01-01';
谢谢我在您的答案中添加了一个查询解决方案。我只是想知道为什么我发布的第一个查询不起作用。