Question

我想在给定字段中选择具有最小值的子查询的所有行。以下是我迄今为止所尝试过的技术的一些玩具示例：

-- 1.
select
    id, min(foo)
from
    (select 1 AS id, 2 AS foo
    union select 2 AS id, 2 AS foo
    union select 3 AS id, 3 AS foo) a;

-- 2.
select
    min(foo)
from
    (     
          select 1 AS id, 2 AS foo, 0 AS const
    union select 2 AS id, 2 AS foo, 0 AS const
    union select 3 AS id, 3 AS foo, 0 AS const) a
group by const;

-- 3.
select
    id
from
    (select 1 AS id, 2 AS foo
    union select 2 AS id, 2 AS foo
    union select 3 AS id, 3 AS foo) a
where id = (select id from a where min(foo) = foo);

-- 4.
select
    id
from
    (select 1 AS id, 2 AS foo
    union select 2 AS id, 2 AS foo
    union select 3 AS id, 3 AS foo) a
where foo = (select min(foo));

-- 5.
select r.*
from
(
    select min(foo) t
    from
        (select 1 AS id, 2 AS foo
        union select 2 AS id, 2 AS foo
        union select 3 AS id, 3 AS foo) a
) m
INNER JOIN a ON m.t = r.foo;

我正在处理的实际查询与示例类似，因为它由UNIONed组成的几个较小的查询组成。这里的总体目标是在中心表中根据与其连接的关联表 k 的字段查找行，其中 k 是最高优先级表。结果是一种来自相似（但不同的表）的行的树视图。

我已经提到了这一点，以防万一有人看到我以迂回的方式解决这个问题，他们可以对大局有所了解。但是现在我的角度是通过在子查询中的字段上取最小值来选择。

Answer 1

使用order by和limit：

select t.*
from t
order by foo
limit 1;

注意：即使存在重复项，这也仅返回最小的一行。 t是您的子查询或表格。

如果你想要所有这些，那么你需要包括两次表定义：

select t.*
from t
where t.foo = (select min(t2.foo) from t t2);

MySQL选择具有最小值的所有子查询行

1 个答案: