+----------+--------+
| stu_name | stu_no |
+----------+--------+
| Abcd     |      1 |
| Acmn     |      1 |
| Borne    |      1 |
| Bence    |      1 |
| Lucy     |      1 |
| Jone     |      2 |
| Lucy     |      2 |
| Lily     |      2 |
+----------+--------+

+----------+--------+
| A        | B      |
+----------+--------+
| 2        |      2 |
+----------+--------+

select count(ta.stu_name) as A, count(tb.stu_name) as B from
    (select stu_name, stu_no from stuInfo where stu_no=1) filtered_table
    left join filtered_table ta on stu_name like 'A%'
    left join filtered_table tb on stu_name like 'B%';

select count(ta.stu_name) as A, count(tb.stu_name) as B from
 (select stu_name, stu_no from stuInfo where stu_no = 1 and stu_name like 'A%') ta left join
(select stu_name, stu_no from stuInfo where stu_no = 1 and stu_name like 'B%') tb;