Question

从这个Mysql表：

Attributes
Brand   |attr   |   vals
Samsung | RAM   |   '750'
Samsung | CPU   |   '1200'
HTC     | RAM   |   '1000'
HTC     | CPU   |   '1500'

我不知道如何使用

获取所有项目

RAM>500
CPU>1300

结果我只需要符合所有参数的品牌：

Attributes
Brand   |attr   |   vals
HTC     | *     |   *

看看SQL小提琴： http://sqlfiddle.com/#!2/491d7/1

Answer 1

我会通过旋转数据获得结果：

select brand, RAM, CPU
from
(
   select brand,
      max(case when attr='RAM' then cast(vals as unsigned) end) as RAM,
      max(case when attr='CPU' then cast(vals as unsigned) end) as CPU
   from attributes
   group by brand
) d
where RAM > 500
  and CPU > 1300

请参阅SQL Fiddle with Demo

Answer 2

最外面的WHERE子句首先限定1300或更多的RAM属性。通过同一品牌再次加入自己（别名“b”），你现在拥有相同的品牌，但这次你只是在CPU上限定“b”属性，它的值> = 500.你可以保持链接任何其他标准的其他JOIN。这是在你正在寻找的所有组件上进行限定...

select
      a.Brand,
      a.vals as RAM,
      b.vals as CPU
   from
      Attributes a
         JOIN Attributes b
            on a.Brand = b.Brand
           AND b.attr = 'CPU'
           AND b.vals >= 1300
   where
          a.attr = 'RAM'
      AND a.vals >= 500

Answer 3

SELECT
    Brand
FROM Attributes
WHERE
    (attr = 'RAM' AND cast(vals as unsigned) > 500)
    OR (attr = 'CPU' AND cast(vals as unsigned) > 1300)
GROUP BY Brand
HAVING COUNT(*) >= 2

Answer 4

更改@ bluefeet的查询，因此没有派生表。它可能会提高某些MySQL版本的效率，但它会破坏ANSI / ISO SQL的有效性，并且不会以ONLY_FULL_GROUP_BY模式运行：

select brand,
  max(case when attr='RAM' then cast(vals as unsigned) end) as RAM,
  max(case when attr='CPU' then cast(vals as unsigned) end) as CPU
from attributes
group by brand  
having RAM > 500
   and CPU > 1300 ;

改进它，所以它也是有效的：

select brand,
  max(case when attr='RAM' then cast(vals as unsigned) end) as RAM,
  max(case when attr='CPU' then cast(vals as unsigned) end) as CPU
from attributes
group by brand  
having max(case when attr='RAM' then cast(vals as unsigned) end) > 500
   and max(case when attr='CPU' then cast(vals as unsigned) end) > 1300 ;

Mysql：多行比较

4 个答案: