Easy MySQL question: query with a null value

Question

What am I doing wrong with this query? (Friday afternoon brain freeze...)

In WordPress, I used a MySQL query to make an empty custom field called "description" in all posts of a test database, and now I want to add the value "test" to that field. (This is all in the process of teaching myself how to write more complex queries.)

But I can't get this query to deal with the fact that the field has no value. 'NULL' doesn't work (and it appears that or IS NULL is what I should be using, according to other stackoverflow answers), and '%' doesn't.

UPDATE `wp_postmeta` SET `meta_value` = replace(meta_value, 'IS NULL', 'test') WHERE `meta_key` LIKE 'description'

Answer 1

I think you want

UPDATE `wp_postmeta` SET `meta_value` = 'test'
 WHERE `meta_key` LIKE 'description'
   and `meta_value` is null

Answer 2

You could try:

UPDATE `wp_postmeta` 
SET `meta_value` = 'test'
WHERE `meta_key` LIKE 'description'
AND `meta_value` IS NULL