Fonction de valeur de table vs fonction de valeurs scalaires pour une valeur de retour unique

Ma discussion avec Jonatha Dickinson (regardez sa réponse) m'a amené à faire quelques tests rapides :

Il en ressort que la sous-sélection scalaire pure et intégrée n'est pas si mal. Interroger une seule valeur, c'est même le plus rapide . Comme prévu, la fonction scalaire est mauvaise. Plus il y a de champs restitués par la TVF, meilleur est le gain relatif de performances.

La seule réponse sûre est :La fonction scalaire est la pire et un TVF multi-ligne est - la plupart du temps - plus lent qu'en ligne. Toute approche ad hoc a tendance à être plus rapide .

Mais je pouvais configurer des cas particuliers pour toutes les situations (à l'exception de la fonction scalaire), où une approche était la plus rapide.

Conclusion :(comme toujours :-) ) Cela dépend...

Astuce :le mieux est de laisser cela aller contre une grande base de données avec de nombreuses tables et colonnes.

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;