SQL Null
NULL is a special value that matches missed data. It means there is no data inserted into the field.
There are operators to detect whether the value is NULL:
IS NULL: detects only values that equal to NULLIS NOT NULL: detects values that are not NULL.
12SELECT title FROM songs WHERE album IS NOT NULL
NULLdoes not match 0 or empty line, it only matches data that is missing and does not exist.
NULLvalues are ignored in theMIN,MAX,COUNT,AVG, andSUMaggregate functions.
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NULL is a special value that matches missed data. It means there is no data inserted into the field.
There are operators to detect whether the value is NULL:
IS NULL: detects only values that equal to NULLIS NOT NULL: detects values that are not NULL.
12SELECT title FROM songs WHERE album IS NOT NULL
NULLdoes not match 0 or empty line, it only matches data that is missing and does not exist.
NULLvalues are ignored in theMIN,MAX,COUNT,AVG, andSUMaggregate functions.
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