Alternatieve methoden 1

De queryprestaties verbeteren in SQL Server

Dean Smith

Founder, Atamai Analytics

EXISTS

SELECT CustomerID,
       CompanyName,
       ContactName 
FROM Customers c
WHERE EXISTS
        (SELECT 1 
         FROM Orders o
         WHERE c.CustomerID = o.CustomerID);

CustomerID	CompanyName	ContactName
ALFKI	Alfreds Futterkiste	Maria Anders
LAUGB	Laughing Bacchus Wine Cellars	Yoshi Tannamuri
QUICK	QUICK-Stop	Horst Kloss
...	...	...

IN

SELECT CustomerID,
       CompanyName,
       ContactName 
FROM Customers
WHERE CustomerID IN
        (SELECT CustomerID 
         FROM Orders);

CustomerID	CompanyName	ContactName
ALFKI	Alfreds Futterkiste	Maria Anders
LAUGB	Laughing Bacchus Wine Cellars	Yoshi Tannamuri
QUICK	QUICK-Stop	Horst Kloss
...	...	...

EXISTS vs. IN

EXISTS stopt met zoeken in de subquery zodra de voorwaarde TRUE is

IN verzamelt alle resultaten uit een subquery voordat ze naar de buitenste query gaan

Overweeg EXISTS te gebruiken in plaats van IN met een subquery

NOT EXISTS

SELECT CustomerID,
       CompanyName,
       ContactName 
FROM Customers c
WHERE NOT EXISTS 
        (SELECT 1 
         FROM Orders o
         WHERE c.CustomerID = o.CustomerID);

CustomerID	CompanyName	ContactName
FISSA	FISSA Fabrica Inter. Salchichas S.A.	Diego Roel
PARIS	Paris spécialités	Marie Bertrand

NOT IN

SELECT CustomerID,
       CompanyName,
       ContactName 
FROM Customers
WHERE CustomerID NOT IN
        (SELECT CustomerID 
         FROM Orders);

CustomeID	CompanyName	ContactName
FISSA	FISSA Fabrica Inter. Salchichas S.A.	Diego Roel
PARIS	Paris spécialités	Marie Bertrand

NOT IN en NULL-waarden

SELECT UNStatisticalRegion AS UN_Region
      ,CountryName
      ,Capital
FROM Nations
WHERE Capital NOT IN 
        (SELECT NearestPop 
         FROM Earthquakes);

UN_Region	CountryName	Capital

NOT IN met NULLs afhandelen

SELECT UNStatisticalRegion AS UN_Region
      ,CountryName
      ,Capital
FROM Nations
WHERE Capital NOT IN 
        (SELECT NearestPop 
         FROM Earthquakes
         WHERE NearestPop IS NOT NULL);

UN_Region	CountryName	Capital
South Asia	India	New Delhi
East Asia and Pacific	Indonesia	Jakarta
East Asia and Pacific	East Timor	Dili
Sahara Africa	Comoros	Moroni
...	...	...

EXISTS, NOT EXISTS, IN en NOT IN

Voordelen

Resultaten kunnen elke kolom uit de buitenste query bevatten, in elke volgorde

Nadelen

Hoe NOT IN omgaat met NULL-waarden in de subquery

Laten we oefenen!

De queryprestaties verbeteren in SQL Server