How to count NULL values in MySQL?

Question

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 i

Answer 1

I may be missing something mysql specific but this would work in sql server

SELECT COUNT(*) as num
FROM users
WHERE user_id = '$user_id'
AND average IS NULL

Answer 2

Also, you can:

Select Count(*) - Count(Average) as NullAverages
From Users
Where user_id = '$user_id' 

Answer 3

A bit late but you can do it in MySQL 5.0.51:

SELECT COUNT(*) AS total, COUNT(field1) AS notNullFields1
FROM table
GROUP BY field5, field6

Regards.

Answer 4

you're on the right track. Remove '_' from 'IS_NULL' and change 'COUNT(average)' to 'COUNT(1)' and you will have it.

For more information on working with NULL in MYSQL see http://dev.mysql.com/doc/refman/5.0/en/working-with-null.html

And for working with IS NULL specifically see

http://dev.mysql.com/doc/refman/5.0/en/comparison-operators.html#operator_is-null

Answer 5

SELECT
    COUNT(*) as num
FROM
    users
WHERE
    user_id = '$user_id' AND
    average IS NULL

Answer 6

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)...