为什么我的存储过程返回0？

Question

我正在尝试获取pointsEarned列的总和以及pointsPossible列的总和。我想把它变成一个百分比。我的问题是我的SP总是返回0，即使有给定enrollmentId的行具有前一列的值。

我做错了什么？

ALTER PROCEDURE GetPercentage 
    @enrollmentId int
AS
BEGIN
    DECLARE @pointsEarned int;
    DECLARE @pointsPossible int;

    SET NOCOUNT ON;

    SELECT 
        @pointsEarned = CAST(SUM(pointsEarned) OVER() AS decimal), 
        @pointsPossible = CAST(SUM(pointsPossible) OVER() AS decimal)
    FROM 
        Assignments
    WHERE 
        enrollmentId = @enrollmentId

    RETURN @pointsEarned / @pointsPossible
END
GO

这是数据库表：

我执行存储过程并传入69的enrollmentId，它仍然返回0.

Answer 1

分母（pointsPossible）大于分子（pointsEarned）的整数除法返回零。

写为（修订）：

ALTER PROCEDURE GetPercentage 
    @enrollmentId int
AS
BEGIN
    SET NOCOUNT ON;

    SELECT 
        Percent = case when sum(pointsPossible) > 0 then (1.0 * sum(pointsEarned)) / sum(pointsPossible) else 0 end
    FROM 
        Assignments
    WHERE 
        enrollmentId = @enrollmentId
    GROUP BY
        enrollmentId 
END
GO

正如@ Nick.McDermaid指出的那样，由于此过程返回标量值，因此将其定义为函数而不是存储过程可能更合适。

Answer 2

1. 使用不含SUM的简单OVER。

2. RETURN只能返回int。如果您的百分比小于100％，整数除法将始终返回0，因此乘以100以返回整数百分比而不是比率。

3. 检查您是否没有除以零。

<强>程序

ALTER PROCEDURE GetPercentage 
    @enrollmentId int
AS
BEGIN
    SET NOCOUNT ON;

    DECLARE @pointsEarned int;
    DECLARE @pointsPossible int;

    SELECT 
        @pointsEarned = SUM(pointsEarned),
        @pointsPossible = SUM(pointsPossible)
    FROM 
        Assignments
    WHERE 
        enrollmentId = @enrollmentId
    ;

    RETURN 
        CASE WHEN @pointsPossible <> 0
        THEN 100 * @pointsEarned / @pointsPossible
        ELSE 0 END;

END
GO