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SQL Tutorial for Beginners

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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 NULL

  • IS NOT NULL: detects values that are not NULL.

SELECT title FROM songs
WHERE album IS NOT NULL

              
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SELECT title FROM songs
WHERE album IS NOT NULL
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NULL does not match 0 or empty line, it only matches data that is missing and does not exist.

NULL values are ignored in the MIN, MAX, COUNT, AVG, and SUM aggregate functions.

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