Mysql从单个列中选择计数值

Question

A有一个名为key的列 - 1,1,2,2,2,2,3 现在我用3个查询来做：

SELECT count(key) as k FROM `test` WHERE key=1
SELECT count(key) as k FROM `test` WHERE key=2
SELECT count(key) as k FROM `test` WHERE key=3

如何在一个查询中统计有多少1,2,3？

Answer 1

使用group by：

SELECT `key`, COUNT(*) FROM `test` GROUP BY `key`;

Answer 2

你可以这样做

select count(key) as K FROM test where key in (1,2,3)

Answer 3

这是另一种选择：

SELECT sum(key=1) as k1, sum(key=2) as k2,sum(key=3) as k3 FROM `test`

如果key的值是某个其他组的一部分，您还可以按列添加组。

Answer 4

试试这个

SELECT  COUNT(Key) as K
        FROM 
        test 
        GROUP BY Key