Mysql子查询问题

Question

给定这两个表：

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

我怎样才能找到所有 Foo.names 没有对应的地方 Bar,value 高于 0？

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

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 2

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

该查询和 zodeus 发布的查询执行时间大约相同，但是该查询不会包含 Bar 表未引用的任何 Foo 记录。例如，如果您还有记录 Foo ( 4, d )，则此查询仍将返回“b”，而 zodeus 的查询将返回“b”和“d”。

Answer 3

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

Answer 4

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