在mysql中选择多个计数

Question

MySQL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，一个是一切，以及一个匹配WHERE子句的东西吗？

Answer 1

如果你的数据库支持CASE WHEN语句，这将有效，否则你仍然会得到基本的想法。

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

Answer 2

它应该像这样SELECT COUNT(*) as totalcount, (SELECT COUNT(*) WHERE foo IS NULL) as conditional_count FROM baz这是一个单一的查询，但在

中有子查询

Answer 3

SELECT count（）为totalcount， （选择COUNT（）FROM baz WHERE foo IS NULL） as conditional_count FROM baz;

我不能在计数括号之间放置星号（*）！ 我说，但我无法显示它。

Answer 4

尝试使用UNION（未测试）

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

Answer 5

我不认为这是可能的。我估计你需要两个查询。

Select count(*) from baz

Select count(foo) from baz where foo is null