行数MySQL的三个用表

Question

我的MySQL数据库看起来像这样

**table_schools** 
id | name 
1 | school_1 
2 | school_2 

**table_classes** 
id | class | school_id 
1 | a  | 1 
2 | b  | 1 
3 | c  | 2 
4 | d  | 2 
5 | e  | 2 

**table_students** 
id | name | class_id 
1 | Nick | 1 
2 | Tom | 2 
3 | Kevin | 3 
4 | Jane | 4 
5 | Mark | 5 
6 | Tim | 5 
7 | Lynn | 5 

我想有一个像这样的输出：

school_name | class_count | student_count 
school_1 | 2   | 2 
school_2 | 3   | 5 

有没有办法在一条SQL查询来做到这一点？如何？

Answer 1

SELECT s.name, COUNT(DISTINCT c.id) AS classes, COUNT(st.id) AS students 
FROM table_schools s 
LEFT JOIN 
     table_classes c 
ON  c.school_id = s.id 
LEFT JOIN 
     table_students st 
ON  st.class_id = c.id 
GROUP BY 
     s.id 

Answer 2

SELECT table_schools.name, COUNT(table_classes.name) AS classes, COUNT(table_students.id) AS students 
FROM table_schools 
LEFT JOIN table_classes ON table_schools.id = table_classes.school_id 
LEFT JOIN table_students ON table_students.class_id = table_classes.id 
GROUP BY table_schools.id, table_classes.id 
ORDER BY table_schools.name