Question

鉴于这两个表：

Foo (id, name)       -- PK = id
Bar (fooId, value)   -- PK = composite, fooId + value
                     -- value is a non-negative int

如何找到0 {/ p>以上没有对应Foo.name的所有Bar,value？

例如：

Foo
id   name
1    a
2    b
3    c

Bar
fooid    value
1        0
1        1
2        0
3        4

Result:
b

Answer 1

SELECT Name
FROM Bar
INNER JOIN Foo ON Foo.Id = Bar.fooId
GROUP BY fooId, name
HAVING SUM(Value) = 0

此查询和zodeus发布的查询大约需要相同的执行时间，但是这个查询不会包含任何未被Bar表引用的Foo记录。例如，如果你还有记录Foo（4，d），这个查询仍将返回'b'，因为zodeus的查询将返回'b'和'd'。

Answer 2

SELECT name FROM FOO WHERE id NOT IN(
    SELECT fooId FROM Bar GROUP BY fooId HAVING MAX(Value) > 0)

Answer 3

我发现以下内容最容易阅读和理解......

SELECT foo.name
FROM foo
WHERE NOT EXISTS (SELECT 'x'
                  FROM bar
                  WHERE bar.fooid = foo.id
                    AND bar.value > 0)

Answer 4

select Foo.name 
from Foo
where Foo.id not in 
(select Bar.fooid from Bar
where value > 0)

Mysql子查询问题

4 个答案: