查询多行SQL Where子句

需要一个查询的帮助，该查询基于某些条件从多行获取结果。例如，我们有一张有[卷号]和[主题]的桌子。对于同一个[卷号]，表可以有多条记录。我的要求是，如果学生只选择“英语”，那么结果应该返回“E”，如果数学，那么返回“M”，如果两者都选择，那么返回“B”。

//我想这就是你想要的

INSERT INTO dbo.rolls
    ( name, subject )
VALUES  ( 'Jones', 'English'),
( 'Smith', 'Math'),
('Adams','English'),
('Adams', 'Math')
GO

;WITH CTE AS (
SELECT subquery1.name, 'B' AS code FROM (
SELECT name,COUNT(name) AS cnt
FROM rolls
WHERE subject = 'English' OR subject = 'Math'
GROUP BY name
HAVING COUNT(name) > 1 ) AS subquery1

UNION 

SELECT subquery2.name, SUBSTRING(rolls.subject,1,1) AS code FROM (
SELECT name,COUNT(name) AS cnt
FROM rolls
WHERE subject = 'English' OR subject = 'Math'
GROUP BY name
HAVING COUNT(name) = 1 ) AS subquery2
INNER JOIN dbo.rolls
ON rolls.name = subquery2.name
)

SELECT * FROM CTE

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你试过什么？这是一个具有条件逻辑的非常基本的聚合查询。添加示例表数据和预期结果。