用于获取记录的条件 WHERE 子句

Question

我正在使用 SQL Server 2008 R2。

我有一个如下的 SQL 块：

DECLARE @Day INT = 5
DECLARE @Month INT = NULL
DECLARE @year INT = NULL
DECLARE @dtnow DATETIME

SET @dtnow = GETDATE()

IF @Month IS NULL
    SELECT @Month = MONTH(DATEADD(MONTH,-1, @dtnow ))

IF @Year IS NULL
    SELECT @year = YEAR(DATEADD(MONTH,-1, @dtnow ))


SELECT * 
FROM TblSalesRecords 
WHERE 
    CASE WHEN @Day IS NULL THEN -- Condition One
        BEGIN 
            ISNULL(@Month, MONTH(TblSalesRecords.CreatedDate)) = MONTH(TblSalesRecords.CreatedDate) 
            AND (@year, YEAR(TblSalesRecords.CreatedDate)) = YEAR(TblSalesRecords.CreatedDate)
        END 
    ELSE                        -- Condition two
        BEGIN 
            TblSalesRecords.CreatedDate BETWEEN CONVERT(DATETIME, CONVERT(VARCHAR,YEAR(DATEADD(MONTH,-1, @dtnow ))) + '-' + CONVERT(VARCHAR,month(DATEADD(MONTH,-1,@dtnow))) + '-' + CONVERT(VARCHAR, DAY(DATEADD(MONTH,-1,@dtnow))) +' 00:00:00.000') 
            AND CONVERT (DATETIME, CONVERT(VARCHAR,YEAR(DATEADD(DAY,-1,@dtnow ))) + '-' + CONVERT(VARCHAR,MONTH(DATEADD(DAY,-1,@dtnow))) + '-' + CONVERT(VARCHAR, DAY(DATEADD(DAY,-1,@dtnow))) +' 23:59:59.998')
        END
    END 
    AND TblSalesRecords.IsDeleted=0

我想要实现的是，

如果@Day设置为NULL，那么它应该执行的CASE..WHEN语句--条件一 else --条件二。

但在CASE..WHEN 语句中，"=" 附近出现语法错误。

谁能告诉我如何做到这一点？

Answer 1

你可以这样实现：

SELECT * 
FROM TblSalesRecords 
WHERE (@Day IS NULL 
            AND ISNULL(@Month, MONTH(TblSalesRecords.CreatedDate)) = MONTH(TblSalesRecords.CreatedDate) 
            AND (@year, YEAR(TblSalesRecords.CreatedDate)) = YEAR(TblSalesRecords.CreatedDate)
       )
    OR (@Day IS NOT NULL                      -- Condition two
            AND TblSalesRecords.CreatedDate BETWEEN CONVERT(DATETIME, CONVERT(VARCHAR,YEAR(DATEADD(MONTH,-1, @dtnow ))) + '-' + CONVERT(VARCHAR,month(DATEADD(MONTH,-1,@dtnow))) + '-' + CONVERT(VARCHAR, DAY(DATEADD(MONTH,-1,@dtnow))) +' 00:00:00.000') 
            AND CONVERT (DATETIME, CONVERT(VARCHAR,YEAR(DATEADD(DAY,-1,@dtnow ))) + '-' + CONVERT(VARCHAR,MONTH(DATEADD(DAY,-1,@dtnow))) + '-' + CONVERT(VARCHAR, DAY(DATEADD(DAY,-1,@dtnow))) +' 23:59:59.998')
        )
    AND TblSalesRecords.IsDeleted=0

(@year, YEAR(TblSalesRecords.CreatedDate)) = YEAR(TblSalesRecords.CreatedDate) 中还有另一个语法错误，但我不确定应该是什么，所以我保持原样。