Min diskussion med Jonatha Dickinson (titta på hans svar) fick mig att göra några snabba tester:
Det kommer fram att den rena, inbäddade skalära undervalet är inte så illa. Om du frågar bara ett värde är det till och med det snabbaste . Som väntat är den skalära funktionen dålig. Ju fler fält som ges tillbaka av TVF desto bättre är den relativa prestandavinsten.
Det enda säkra svaret är:Den skalära funktionen är den sämsta och en multi-line TVF är - för det mesta - långsammare än inline. Alla ad hoc-metoder tenderar att vara snabbare .
Men jag kunde ställa in specialfall för alla situationer (förutom den skalära funktionen), där ett tillvägagångssätt var snabbast.
Slutsats:(som alltid :-) ) Det beror på...
Tips:Bäst är att låta detta gå mot en stor databas med många tabeller och kolumner.
CREATE FUNCTION dbo.CountColumnScalar(@TableSchema AS VARCHAR(100),@TableName AS VARCHAR(100))
RETURNS INT
AS
BEGIN
RETURN(SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS AS c WHERE [email protected] AND [email protected]);
END
GO
CREATE FUNCTION dbo.CountConstraintScalar(@TableSchema AS VARCHAR(100),@TableName AS VARCHAR(100))
RETURNS INT
AS
BEGIN
RETURN(SELECT COUNT(*) FROM INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE AS c WHERE [email protected] AND [email protected]);
END
GO
CREATE FUNCTION dbo.CountAllTVF(@TableSchema AS VARCHAR(100),@TableName AS VARCHAR(100))
RETURNS TABLE
RETURN SELECT (SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS AS c WHERE [email protected] AND [email protected] GROUP BY c.TABLE_SCHEMA,c.TABLE_NAME) AS ColCounter
,(SELECT COUNT(*) FROM INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE AS c WHERE [email protected] AND [email protected] GROUP BY c.TABLE_SCHEMA,c.TABLE_NAME) AS ConstraintCounter ;
GO
CREATE FUNCTION dbo.CountAllTVF_multiline(@TableSchema AS VARCHAR(100),@TableName AS VARCHAR(100))
RETURNS @tbl TABLE (ColCounter INT,ConstraintCounter INT)
AS
BEGIN
INSERT INTO @tbl
SELECT (SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS AS c WHERE [email protected] AND [email protected] GROUP BY c.TABLE_SCHEMA,c.TABLE_NAME) AS ColCounter
,(SELECT COUNT(*) FROM INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE AS c WHERE [email protected] AND [email protected] GROUP BY c.TABLE_SCHEMA,c.TABLE_NAME) AS ConstraintCounter;
RETURN;
END
GO
DECLARE @time DATETIME=GETDATE();
SELECT TABLE_SCHEMA,TABLE_NAME
,(SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS AS c WHERE c.TABLE_SCHEMA=t.TABLE_SCHEMA AND c.TABLE_NAME=t.TABLE_NAME ) AS ColCounter
,(SELECT COUNT(*) FROM INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE AS c WHERE c.TABLE_SCHEMA=t.TABLE_SCHEMA AND c.TABLE_NAME=t.TABLE_NAME ) AS ConstraintCounter
FROM INFORMATION_SCHEMA.TABLES AS t;
PRINT 'pure embedded scalar sub-select: ' + CAST(CAST(GETDATE()[email protected] AS TIME) AS VARCHAR(MAX)); SET @time=GETDATE();
SELECT TABLE_SCHEMA,TABLE_NAME
,dbo.CountColumnScalar(t.TABLE_SCHEMA,t.TABLE_NAME ) AS ColCounter
,dbo.CountConstraintScalar(t.TABLE_SCHEMA,t.TABLE_NAME ) AS ConstraintCount
FROM INFORMATION_SCHEMA.TABLES AS t
PRINT 'scalar function: ' + CAST(CAST(GETDATE()[email protected] AS TIME) AS VARCHAR(MAX)); SET @time=GETDATE();
SELECT t.TABLE_SCHEMA,t.TABLE_NAME
,colJoin.ColCount
,conJoin.ConstraintCount
FROM INFORMATION_SCHEMA.TABLES AS t
INNER JOIN (SELECT COUNT(*) As ColCount,c.TABLE_SCHEMA,c.TABLE_NAME
FROM INFORMATION_SCHEMA.COLUMNS AS c
GROUP BY c.TABLE_SCHEMA,c.TABLE_NAME) AS colJoin ON colJoin.TABLE_SCHEMA=t.TABLE_SCHEMA AND colJoin.TABLE_NAME=t.TABLE_NAME
INNER JOIN (SELECT COUNT(*) As ConstraintCount,c.TABLE_SCHEMA,c.TABLE_NAME
FROM INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE AS c
GROUP BY c.TABLE_SCHEMA,c.TABLE_NAME) AS conJoin ON conJoin.TABLE_SCHEMA=t.TABLE_SCHEMA AND conJoin.TABLE_NAME=t.TABLE_NAME
PRINT 'JOINs on sub-selects: ' + CAST(CAST(GETDATE()[email protected] AS TIME) AS VARCHAR(MAX)); SET @time=GETDATE();
SELECT t.TABLE_SCHEMA,t.TABLE_NAME
,ColCounter.*
FROM INFORMATION_SCHEMA.TABLES AS t
CROSS APPLY dbo.CountAllTVF(t.TABLE_SCHEMA,t.TABLE_NAME) AS ColCounter
PRINT 'TVF inline: ' + CAST(CAST(GETDATE()[email protected] AS TIME) AS VARCHAR(MAX)); SET @time=GETDATE();
SELECT t.TABLE_SCHEMA,t.TABLE_NAME
,ColCounter.*
FROM INFORMATION_SCHEMA.TABLES AS t
CROSS APPLY dbo.CountAllTVF_multiline(t.TABLE_SCHEMA,t.TABLE_NAME) AS ColCounter
PRINT 'TVF multiline: ' + CAST(CAST(GETDATE()[email protected] AS TIME) AS VARCHAR(MAX)); SET @time=GETDATE();
GO
DROP FUNCTION dbo.CountColumnScalar;
DROP FUNCTION dbo.CountAllTVF;
DROP FUNCTION dbo.CountAllTVF_multiline;
DROP FUNCTION dbo.CountConstraintScalar;