(sum(if(s_score >= 60, 1, 0)) / (select count(*) from student)) * 100 生么意思

这是一个 SQL 查询语句，它的意思是：统计成绩大于等于60分的学生人数并除以总学生人数，然后乘以100，得到及格率的百分比。其中，if(s_score >= 60, 1, 0) 是一个条件语句，表示如果s_score（学生分数）大于等于60，返回1，否则返回0；sum() 函数用于求和，count(*) 函数用于统计总行数。

相关问题

select a.s_id ,a.s_name ,count(b.c_id) as sum_course ,sum(b.s_score)as sum_score from student a left join score b on a.s_id=b.s_id GROUP BY a.s_id,a.s_name

Sure! Here is the SQL query to fulfill your request:

SELECT a.s_id, a.s_name, COUNT(b.c_id) AS sum_course, SUM(b.s_score) AS sum_score
FROM student a
LEFT JOIN score b ON a.s_id = b.s_id
GROUP BY a.s_id, a.s_name;

This query will retrieve the student ID (`s_id`), student name (`s_name`), the total number of courses taken by each student (`sum_course`), and the sum of scores obtained by each student (`sum_score`). The `LEFT JOIN` ensures that all students are included in the result, even if they don't have any scores recorded in the `score` table.

Let me know if you need any further assistance!

为何这段代码会出现部分行重复出现的问题：select s.s_id,count(1) 选课数,sum(s_score) 总分 from student s join score c on s.s_id=c.s_id group by s.s_id

这段代码中出现部分行重复的问题是因为使用了JOIN操作，导致在结果集中出现了多对一的关系。

在你的代码中，通过`JOIN`操作将`student`表和`score`表连接在一起，然后使用`GROUP BY`对`s.s_id`进行分组。当一个学生在`score`表中有多条记录时，会导致多个行与同一个学生ID相关联，并且进行聚合计算。

例如，如果一个学生在`score`表中有3条记录，那么在执行`COUNT(1)`和`SUM(s_score)`时，该学生的数据将会出现3次，导致部分行重复。

要解决这个问题，你可以在连接之前先对`score`表进行汇总，然后再与`student`表进行连接。这样可以确保每个学生只有一行数据参与聚合计算。以下是修改后的代码：

SELECT s.s_id, COUNT(c.s_id) AS 选课数, SUM(c.s_score) AS 总分
FROM student s
JOIN (
    SELECT s_id, s_score
    FROM score
    GROUP BY s_id, s_score
) c ON s.s_id = c.s_id
GROUP BY s.s_id

这样，结果集中每个学生将只出现一次，并且得到正确的选课数和总分。