123123

#1 Created at ... [Delete] [Delete and Lock User]

要显示这种格式的怎么实现？

班级人数一班 4 二班 3 三班 3

#2 Created at ... [Delete] [Delete and Lock User]

SELECT class_id, COUNT(name) num FROM students GROUP BY class_id;

#3 Created at ... [Delete] [Delete and Lock User]

不对，这个查询返回的是id号，不是班级名称

#4 Created at ... [Delete] [Delete and Lock User]

select count(c.name),c.* from students a left join classes c on a.class_id = c.id group by c.id

#5 Created at ... [Delete] [Delete and Lock User]

SELECT classes.name,COUNT(classes.name) num FROM students, classes WHERE students.class_id = classes.id GROUP BY classes.name;

#6 Created at ... [Delete] [Delete and Lock User]

select class_id,count(id) from students group by class_id;

#7 Created at ... [Delete] [Delete and Lock User]

SELECT c.name, COUNT(*) num FROM students s,classes c where s.class_id = c.id GROUP BY c.name;