Question

我将尽可能简化这一过程。经过数小时的调试，我发现了DRASTIC速度下降的根源。

DECLARE @Id INT = 9999

SELECT * 
FROM dbo.FN_Whatever(@Id, NULL, NULL)

执行时间：15分钟

SELECT * 
FROM dbo.FN_Whatever(9999, NULL, NULL)

执行时间：0秒

请帮助我了解这个令人沮丧的问题...

以下是该功能的摘要（私人公司代码等等）

CREATE FUNCTION FN_Whatever
    (@Id INT,
     @V1 INT = NULL,
     @V2 INT = NULL)
RETURNS TABLE
AS
    RETURN 
        SELECT T1.Id, T1.Value
        FROM Table T1
        LEFT JOIN (SELECT X
                   FROM Table T2
                   WHERE Id = @Id
                     AND (@V1 IS NULL OR x = @V1)
                     AND (@V2 IS NULL OR y = @V2)
                   GROUP BY x, y, z) SH_List ON ...
        JOIN 
            FN_2 (@Id, @V1) FN1 ON ...
        WHERE 
            Id = @Id
            AND (@V1 IS NULL OR x = @V1)
            AND (@V2 IS NULL OR y = @V2)

SQL Server局部变量导致性能问题

0 个答案: