在mysql中选择多个计数

Question

在MySQL中可以做这样的事情:

SELECT COUNT(*) as totalcount, 
       COUNT(*) WHERE foo IS NULL as conditional_count 
  FROM baz

即在单个选择中获取两个计数,一个是什么,以及一个匹配WHERE子句的东西？

Answer 1

如果您的数据库支持CASE WHEN语句,这将有效,否则您仍将获得基本想法.

SELECT COUNT(*), 
       SUM(CASE WHEN FOO IS NULL THEN 1 ELSE 0 END) AS COUNT_CONDITIONAL
  FROM baz