为了进行基准测试,让我们创建一个 1M 行的表:
CREATE TABLE dbo.Numbers(n INT NOT NULL PRIMARY KEY)
GO
DECLARE @i INT;
SET @i = 1;
INSERT INTO dbo.Numbers(n) SELECT 1;
WHILE @i<1024000 BEGIN
INSERT INTO dbo.Numbers(n)
SELECT n + @i FROM dbo.Numbers;
SET @i = @i * 2;
END;
GO
运行简单的内联添加:
SELECT COUNT(*) FROM(
SELECT n,n+1 AS ValuePlusOne
FROM dbo.Numbers
) AS t WHERE ValuePlusOne>0
CPU time = 15 ms, elapsed time = 122 ms.
(1 row(s) affected)
Table 'Numbers'. Scan count 1, logical reads 3521, physical reads 3, read-ahead reads 3498, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
SQL Server Execution Times:
CPU time = 406 ms, elapsed time = 951 ms.
创建一个仅将一个整数加一的标量 UDF,并运行 1M 次:
CREATE FUNCTION dbo.[AddOne]
(
@value int
)
RETURNS int
AS
BEGIN
DECLARE @Result int
SELECT @Result = @value + 1
RETURN @Result
END
GO
SELECT COUNT(*) FROM(
SELECT n,dbo.AddOne(n) AS ValuePlusOne
FROM dbo.Numbers
) AS t WHERE ValuePlusOne>0
CPU time = 15 ms, elapsed time = 122 ms.
(1 row(s) affected)
Table 'Numbers'. Scan count 1, logical reads 3521, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
SQL Server Execution Times:
CPU time = 108313 ms, elapsed time = 295072 ms.
创建一个内联 UDF,它和添加一样快,然后运行 1M 次:
CREATE FUNCTION dbo.[AddOneInline]
(
@value int
)
RETURNS TABLE
AS
RETURN(SELECT @value + 1 AS ValuePlusOne)
GO
SELECT COUNT(*) FROM(
SELECT ValuePlusOne
FROM dbo.Numbers
CROSS APPLY dbo.[AddOneInline](n)
) AS t WHERE ValuePlusOne>0
SQL Server parse and compile time:
CPU time = 0 ms, elapsed time = 35 ms.
(1 row(s) affected)
Table 'Numbers'. Scan count 1, logical reads 3521, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
SQL Server Execution Times:
CPU time = 391 ms, elapsed time = 403 ms.
标量 UDF 与内联 UDF 的性能差异是显而易见的。