How to count NULL values in MySQL?

mysql aggregate-functions
abbr picture abbr · Jun 17, 2010 · Viewed 38k times · Source

I want to know how can i find all the values that are NULL in the MySQL database for example I'm trying to display all the users who don't have an average yet.

Here is the MySQL code.

SELECT COUNT(average) as num
FROM users
WHERE user_id = '$user_id'
AND average IS_NULL

Answer

ircmaxell picture ircmaxell · Jun 17, 2010

A more generic version (that doesn't depend on the where clause and hence limits your overall results):

SELECT 
    SUM(CASE WHEN average IS NULL THEN 1 ELSE 0 END) As null_num, 
    SUM(CASE WHEN average IS NOT NULL THEN 1 ELSE 0 END) AS not_null_num
FROM users

It's not better then the specific queries presented by other answers here, but it can be used in situations where using a limiting where clause is impractical (due to other information being needed)...

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