MySQL从一栏中计算不同的值 [英] MySQL Count distinct values from one column

问题描述

我有一个包含三列的表:

I have a table having three columns:

A   B   C
1   2   2
2   2   2
3   1   1
4   1   2   

我想要计算C等于2但B值不同的那些值的计数

I want the count of those values which have C equal to 2 but with distinct values of B

所以在这种情况下，对于C = 2，计数= 2(B = 2和B = 1)

So in this case for C = 2, count = 2 (B=2 and B=1)

我使用了以下命令:

Select count(*) from mytable where C=2 group by (B)

但它会产生:

count(*)
3

我尝试使用"distinct"，但不能用于从一列中选择

I have tried using "distinct" but it can't be use to select from one column

推荐答案

您尝试过

SELECT COUNT(DISTINCT B) FROM mytable WHERE C = 2;

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