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Question

SELECT    Column_A, SUM(CASE WHEN COLUMN_B = 'x' THEN 1 ELSE 'SET SUM TO 0' END) as total
FROM      table 
GROUP BY  Column_A
ORDER BY  Month 

有没有办法将sum的值设置为0，我试图找到cloumn_B的最后一个连续x值的总和如果连续中断我需要将总和设置为0

Table
ColumnA Column B Month
A        x        1
A        x        2
A        x        3
A        y        4

B        x        1
B        y        2
B        x        3
B        x        4

C        x        1
C        x        2
C        y        3
C        x        4

The expected result is:
A    0
B    2
C    1    

Answer 1

试试这个

SELECT    Column_A, SUM(CASE WHEN COLUMN_B = 'x' THEN 1 ELSE 0 END) as total
FROM      table 
GROUP BY  Column_A
ORDER BY  some_date

SUM不能用于非数字数据类型

如果使用，则会收到错误

  

操作数数据类型char对sum运算符无效。

SELECT    Column_A, ISNULL(CAST(SUM(CASE WHEN COLUMN_B = 'x' THEN 1 END) AS VARCHAR),'SET SUM TO 0') AS total
FROM      table 
GROUP BY  Column_A
ORDER BY  some_date

Answer 2

编辑：

DECLARE @TEMP TABLE (columnA varchar(50), maxMonth int )

INSERT INTO @TEMP (columnA, maxMonth)
SELECT columnA, MAX([Month]) FROM [table]
WHERE columnB != 'x'
GROUP BY columnA

SELECT original.columnA, SUM(CASE when original.[Month] > withMax.maxMonth THEN 1 ELSE 0 END) AS TOTAL 
FROM @TEMP withMax JOIN [table] original ON withMax.columnA = original.columnA
WHERE original.columnB = 'x'
GROUP BY original.columnA

此查询应该适合您。