COUNT CASE and WHEN statement in MySQL

问题

How to use COUNT CASE and WHEN statement in MySQL query, to count when data is NULL and when it is not NULL in one MySQL query?

回答1:

Use:

SELECT SUM(CASE 
             WHEN t.your_column IS NULL THEN 1
             ELSE 0
           END) AS numNull,
       SUM(CASE 
             WHEN t.your_column IS NOT NULL THEN 1
             ELSE 0
           END) AS numNotNull
  FROM YOUR_TABLE t

That will sum up the column NULL & not NULL for the entire table. It's likely you need a GROUP BY clause, depending on needs.

来源：https://stackoverflow.com/questions/5045124/count-case-and-when-statement-in-mysql