在 MySQL 中根据科目在单个列中显示学生成绩?
mysqlmysqli database更新于 2025/10/4 10:52:17
为此，请使用 UNION ALL。
首先我们创建一个表:
mysql> create table DemoTable729 ( StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY, StudentName varchar(100), MySQLMarks int, CMarks int, JavaMarks int ); Query OK, 0 rows affected (0.40 sec)
使用 insert 在表中插入一些记录 command:
mysql> insert into DemoTable729(StudentName,MySQLMarks,CMarks,JavaMarks) values('Chris',94,67,75);
Query OK, 1 row affected (0.21 sec)
mysql> insert into DemoTable729(StudentName,MySQLMarks,CMarks,JavaMarks) values('Robert',45,99,54);
Query OK, 1 row affected (0.18 sec)
mysql> insert into DemoTable729(StudentName,MySQLMarks,CMarks,JavaMarks) values('David',57,89,43);
Query OK, 1 row affected (0.12 sec)
使用 select 语句显示表中的所有记录:
mysql> select *from DemoTable729;
这将产生以下输出 -
+-----------+-------------+------------+--------+-----------+ | StudentId | StudentName | MySQLMarks | CMarks | JavaMarks | +-----------+-------------+------------+--------+-----------+ | 1 | Chris | 94 | 67 | 75 | | 2 | Robert | 45 | 99 | 54 | | 3 | David | 57 | 89 | 43 | +-----------+-------------+------------+--------+-----------+ 3 rows in set (0.00 sec)
以下是在单列中显示学生成绩的查询:
mysql> select StudentId,StudentName,'MySQL' as SubjectName, MySQLMarks as Score from DemoTable729 UNION ALL select StudentId,StudentName, 'C' as SubjectName, CMarks as Score from DemoTable729 UNION ALL select StudentId,StudentName, 'Java' as SubjectName, JavaMarks as Score from DemoTable729;
这将产生以下输出 -
+-----------+-------------+-------------+-------+ | StudentId | StudentName | SubjectName | Score | +-----------+-------------+-------------+-------+ | 1 | Chris | MySQL | 94 | | 2 | Robert | MySQL | 45 | | 3 | David | MySQL | 57 | | 1 | Chris | C | 67 | | 2 | Robert | C | 99 | | 3 | David | C | 89 | | 1 | Chris | Java | 75 | | 2 | Robert | Java | 54 | | 3 | David | Java | 43 | +-----------+-------------+-------------+-------+ 9 rows in set (0.00 sec)
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