Mysql 如何在没有分组依据的情况下使用计数？

我有一张这样的桌子。“科目”列的最后一位数字表示学期

滚 主题 1. MTMG1 2. MTMG3 2. CEMG3 3. MTMG1 3. CEMG3 4. PHSG3 5. MTMG3 5. CEMG3

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加入一个子查询，查找第三学期至少有两门学科的考生

SELECT t1.Roll, t1.Subject
FROM table AS t1
JOIN (
    SELECT Roll
    FROM table
    WHERE RIGHT(Subject, 1) = '3'
    GROUP BY Roll
    HAVING COUNT(*) > 1
) AS t2 ON t1.Roll = t2.Roll
WHERE t1.Subject = 'CEMG3'

---

加入一个子查询，查找第三学期至少有两门学科的考生

SELECT t1.Roll, t1.Subject
FROM table AS t1
JOIN (
    SELECT Roll
    FROM table
    WHERE RIGHT(Subject, 1) = '3'
    GROUP BY Roll
    HAVING COUNT(*) > 1
) AS t2 ON t1.Roll = t2.Roll
WHERE t1.Subject = 'CEMG3'

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您可以使用子查询：

select r.* from registar r where r.subject = "CEMG3" where (select count(*) from registrar r1 where r1.roll = r.roll and right(subject, 1) = '3') > 1;

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请参阅。

您可以使用子查询：

select r.* from registar r where r.subject = "CEMG3" where (select count(*) from registrar r1 where r1.roll = r.roll and right(subject, 1) = '3') > 1;

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请参阅。

不能有两个

WHERE

子句。将它们与

和

组合。使用

右（主题，1）

获取最后一个字符。不能有两个

WHERE

子句。将它们与

和

组合。使用

右键（主题1）

获取最后一个字符。