表：

mysql> select * from gg;
+------+------+-----+-------+
| id   | name | sex | class |
+------+------+-----+-------+
|    1 | 張三 | 男  |     1 |
|    2 | 李四 | 女  |     2 |
|    3 | 王五 | 女  |     1 |
+------+------+-----+-------+
3 rows in set (0.00 sec)

sql語句：

select class,sum(case when sex="男" then 1 else 0 end) as numOfMan,
sum(case when sex="女" then 1 else 0 end) as numOfWoman from gg group by class;
 

結果:

mysql> select class,sum(case when sex="男" then 1 else 0 end) as numOfMan,
    -> sum(case when sex="女" then 1 else 0 end) as numOfWoman from gg group by class;
+-------+----------+------------+
| class | numOfMan | numOfWoman |
+-------+----------+------------+
|     1 |        1 |          1 |
|     2 |        0 |          1 |
+-------+----------+------------+
2 rows in set (0.00 sec)