字符串聚合组并计数一个值

I have table like this.

我有这样的桌子。

 | table                        |
 | class_id| name    | gender   |
 +---------+---------+----------+ 
 |       1 | Jane    |     F    |
 |       1 | John    |     M    |
 |       1 | Tom     |     M    |
 |       1 | Bob     |     M    |
 |       2 | Jack    |     M    |
 |       2 | Kate    |     F    |
 | table