Mysql从单个列中选择计数值

Question

A have a column named key - 1,1,2,2,2,2,3 Now i do it with 3 querys:

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

How to count in one query how many 1,2,3?

Answer 1

使用分组：

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

This is another option:

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

you could also add a group by column if the values of key were part of some other group.

Answer 4

Try this

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