Question

我在MYSQL中有这个表：

Year    Type    Value  ID

0       0       5      1
2010    1       6      1
2011    1       4      1
2012    1       5      1
2013    1       7      1
2014    1       8      1
2015    1       5      1
0       0       6      2
2009    1       7      2
2010    1       4      2
2011    1       2      2
2012    1       8      2
2013    1       8      2
2014    1       5      2

我想为每个人选择最小和最大年份（ID 1和2），但我也想为每个人选择与类型0相关联的值。理想情况下，这就是查询结果：

ID   MinYear    MaxYear    Type0Value
1    2010       2015       5
2    2009       2014       6

我认为查询应该是这样的......

select ID, 
(min(year) where type = 1) as MinYear, 
(max(year) where type = 1) as MaxYear,
(value where type = 0) as Type0Value
from table
group by ID

但这显然不是正确的SQL语法。我该怎么做？

Answer 1

奇怪的表结构，但是：

select
    _type0.id,
    _type0.value,
    _type1._min,
    _type1._max
from
    tbl as _type0
    inner join (
        select
            id,
            min(year) as _min,
            max(year) as _max
        from
            tbl
        where
            1 = type
        group by
            id
    ) as _type1 on
        _type0.id = _type1.id
where
    0 = _type0.type;

Answer 2

你应该使用内部联接。一半将处理最小值和最大值，后半部分将处理type0值：

select a.minYear, a.maxYear, a.id, b.type0value from 
(select min(year) as minYear, max(year) as maxYear, id from table where id = 1 group by id) as a
inner join table as b on a.id = b.id 
where b.type = 0

Answer 3

你的伪代码实际上非常接近。你只需要条件聚合：

select ID, 
       min(case when type = 1 then year end) as MinYear, 
       max(case when type = 1 then year end) as MaxYear,
       max(case when type = 0 then value end) as Type0Value
from table
group by ID;

如果type = 0行可能有多行，您可能需要group_concat()代替。

MYSQL - 仅将where子句应用于某些字段

3 个答案: