查明是否存在按SQL中的值分组的值

我有一张像这样的桌子：

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

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

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

如何构造类似以下内容的select语句：

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

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

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

结果如下所示：

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

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

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

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我不知道如何判断这些项目是否存在，因为它们分散在一行中；我只希望每个客户返回一行

足够近。使用聚合函数

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

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聪明的我担心我会做一些像pivot这样的傻事。非常感谢。