白眉大叔 mysql 数据库case判断语句
case when 条件 then 结果 end
mysql> select teacher.tname,course.cname,concat(floor(count(case when sc.score>=60 then 1 end)/count(*)*100),"%") from teacher
join course on teacher.tno=course.tno
join sc on course.cno=sc.cno
group by teacher.tno,course.cno;
+--------+--------+--------------------------------------------------------------------------+
| tname | cname | concat(floor(count(case when sc.score>=60 then 1 end)/count(*)*100),"%") |
+--------+--------+--------------------------------------------------------------------------+
| oldboy | linux | 100% |
| xiaoQ | python | 66% |
| xiaoA | mysql | 75% |
+--------+--------+--------------------------------------------------------------------------+
3 rows in set (0.00 sec)
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