plsql数据库里 select from where group by having order by

Question

都用上 组成一个查询语句 现在有3个表 student表 有2个列 studentid和studentname。 score表 有3个列
studentid subjectid score。subjectid 有2个列 subjectid subjectname

Answer 1

比如说查询学生A上过的每门课有多少人及格,按从大到小排列
select count(b.studentid) from subjectid a left join score b on a.subjectid=b.subjectid left join student c on b.studentid=c.studentid where c.studentname='A' group by a.subjectid having b.score>60 order by count(b.studentid) desc追问

能解释一下吗？ 我没有学过left join啊