SQL NULL ֵ

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½ IS NULL IS NOT NULL

SQL NULL ֵ

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NULL ֵĴʽֵͬ

NULL δ֪Ļõֵռλ

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SQL NULL ֵ

뿴 "Persons"

Id LastName FirstName Address City
1 Adams John   London
2 Bush George Fifth Avenue New York
3 Carter Thomas   Beijing

"Persons" е "Address" ǿѡġζ "Address" вһֵļ¼"Address" лʹ NULL ֵ档

ôβ NULL ֵأ

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DZʹ IS NULL IS NOT NULL

SQL IS NULL

νѡȡ "Address" д NULL ֵļ¼أ

DZʹ IS NULL

SELECT LastName,FirstName,Address FROM Persons
WHERE Address IS NULL

LastName FirstName Address
Adams John  
Carter Thomas  

ʾʼʹ IS NULL NULL ֵ

SQL IS NOT NULL

ѡȡ "Address" в NULL ֵļ¼أ

DZʹ IS NOT NULL

SELECT LastName,FirstName,Address FROM Persons
WHERE Address IS NOT NULL

LastName FirstName Address
Bush George Fifth Avenue

һУ˽ ISNULL()NVL()IFNULL() COALESCE()