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.
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1
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SELECT title FROM songs
WHERE album IS NOT NULL
12SELECT title FROM songs WHERE album IS NOT NULL
NULL
does not match 0 or empty line, it only matches data that is missing and does not exist.
NULL
values are ignored in theMIN
,MAX
,COUNT
,AVG
, andSUM
aggregate functions.
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