Question

我需要重写以下两个查询以避免OR @MyParam IS NULL检查（使用CASE is not working properly中提到的CASE语句）

是否可以以该格式重写以下查询？

注意：How to pass string parameter with `IN` operator in stored procedure SQL Server 2008

中提供了fn_Split功能

DECLARE @MyParam VARCHAR(MAX)
SET @MyParam = '2,3'

DECLARE @MyTable TABLE (EmpID INT)

INSERT INTO @MyTable VALUES (1)
INSERT INTO @MyTable VALUES (2)
INSERT INTO @MyTable VALUES (3)
INSERT INTO @MyTable VALUES (4)


--Query 1
SELECT * 
FROM @MyTable M
WHERE (
        M.EmpID IN (SELECT CONVERT(int,Value) FROM fn_Split(@MyParam, ','))
        OR @MyParam IS NULL
       )


--Query 2
SELECT * 
FROM @MyTable M
WHERE (EXISTS   (
                  SELECT CONVERT(int,Value) 
                  FROM fn_Split(@MyParam, ',')
                  WHERE CONVERT(int,Value)  =  M.EmpID
                  )
                  OR @MyParam IS NULL
       )

Answer 1

使用左连接

SELECT m.* 
FROM @MyTable M
    left join (SELECT CONVERT(int,Value) v FROM fn_Split(@MyParam, ',')) t 
on m.EmpID = t.v 
where v is not null or @MyParam is null

理想情况下，您不会将包含多个值的字符串作为参数传递 - 如果这是一个存储过程，请使用table valued parameter

使用CASE语句重写查询

1 个答案: