如何在T-SQL中编写选择案例

Question

如何在t-sql中编写select case语句？下面的我的代码不起作用,帮助我只想要匹配大小写,插入语句开始将值插入表中.

SET @DayName = dbo.GetWeekDayNameOfDate(@SaleDate)
      SELECT 
            CASE @DayName
                WHEN 'Sunday' THEN 
                    INSERT INTO Tmp_Data(ProductID,ProductName,Sunday,NetProfit) 
                    VALUES(@ProductId,@ProductName,@Qty,@Profit);
                WHEN 'Monday' THEN 
                    INSERT INTO Tmp_Data(ProductID,ProductName,Monday,NetProfit) 
                    VALUES(@ProductId,@ProductName,@Qty,@Profit);
                WHEN 'Tuesday' THEN 
                    INSERT INTO Tmp_Data(ProductID,ProductName,Tuesday,NetProfit) 
                    VALUES(@ProductId,@ProductName,@Qty,@Profit);
                WHEN 'Wednesday' THEN 
                    INSERT INTO Tmp_Data(ProductID,ProductName,Wednesday,NetProfit) 
                    VALUES(@ProductId,@ProductName,@Qty,@Profit);
                WHEN 'Thursday' THEN 
                    INSERT INTO Tmp_Data(ProductID,ProductName,Thursday,NetProfit) 
                    VALUES(@ProductId,@ProductName,@Qty,@Profit);
                WHEN 'Friday' THEN 
                    INSERT INTO Tmp_Data(ProductID,ProductName,Friday,NetProfit) 
                    VALUES(@ProductId,@ProductName,@Qty,@Profit);
                WHEN 'Saturday' THEN 
                    INSERT INTO Tmp_Data(ProductID,ProductName,Saturday,NetProfit) 
                    VALUES(@ProductId,@ProductName,@Qty,@Profit);
            END

Answer 1

我同意@John Dewey的评论 - 你不应该在每个工作日都有一个专栏,而是一个有工作日的专栏.假设您无法修复损坏的模式,接下来您需要了解这CASE是一个返回值的表达式,而不是像其它语言一样的流语句控件.这意味着你不能说CASE THEN something THEN go do something else.

这是编写语句的一种方法,它将至少减少您尝试的一些冗余:

SET @DayName = dbo.GetWeekDayNameOfDate(@SaleDate);

INSERT dbo.Tmp_Data(ProductID,ProductName,NetProfit,
    Sunday,Monday,Tuesday,Wednesday,Thursday,Friday,Saturday)
    SELECT @ProductId,@ProductName,@Profit,
      CASE @DayName WHEN 'Sunday'    THEN @Qty END,
      CASE @DayName WHEN 'Monday'    THEN @Qty END,
      CASE @DayName WHEN 'Tuesday'   THEN @Qty END,
      CASE @DayName WHEN 'Wednesday' THEN @Qty END,
      CASE @DayName WHEN 'Thursday'  THEN @Qty END,
      CASE @DayName WHEN 'Friday'    THEN @Qty END,
      CASE @DayName WHEN 'Saturday'  THEN @Qty END;

您还可以在动态SQL中构建语句.不是我喜欢的方式,只是为了简洁而包括该选项.

SET @DayName = dbo.GetWeekDayNameOfDate(@SaleDate);

DECLARE @sql NVARCHAR(4000);

SET @sql = N'INSERT dbo.Tmp_Data(ProductID,ProductName,NetProfit,' 
    + @DayName + ') SELECT ' 
      + CONVERT(VARCHAR(12), @ProductId) +','
      + '''' + @ProductName + ''','
      + CONVERT(VARCHAR(12), @Profit) + ','
      + CONVERT(VARCHAR(12), @Qty) + ';';

PRINT @sql;
-- EXEC sp_executesql @sql;