Question

我有一张看起来像这样的表：

CustomerID   ItemType
001          'a'
001          'b'
001          'c'
001          'd'
002          'd'

如何构造类似于以下内容的select语句：

CASE WHEN ItemType = 'a' THEN 1 ELSE 0 END as Aexists, 
CASE WHEN ItemType = 'b' THEN 1 ELSE 0 END as Bexists, 
CASE WHEN ItemType = 'c' THEN 1 ELSE 0 END as Cexists, 
CASE WHEN ItemType = 'd' THEN 1 ELSE 0 END as Dexists,
CASE WHEN ItemType = 'e' THEN 1 ELSE 0 END as Eexists,
GROUP BY CustomerID

结果如下所示：

CustomerID, Aexists, Bexists, Cexists, Dexists, Eexists
001         1        1        1        1        0 
002         0        0        0        1        0

我很困惑如何判断这些物品是否存在，因为它们分布在各行上;我只希望每个客户返回一行。

Answer 1

足够近。使用汇总函数MAX

select
    CustomerID,
    max(CASE WHEN ItemType = 'a' THEN 1 ELSE 0 END) as Aexists, 
    max(CASE WHEN ItemType = 'b' THEN 1 ELSE 0 END) as Bexists, 
    max(CASE WHEN ItemType = 'c' THEN 1 ELSE 0 END) as Cexists, 
    max(CASE WHEN ItemType = 'd' THEN 1 ELSE 0 END) as Dexists,
    max(CASE WHEN ItemType = 'e' THEN 1 ELSE 0 END) as Eexists
from t
GROUP BY CustomerID

找出是否存在按SQL中的值分组的值

1 个答案: