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法律研究如何根据 MySQL 中的科目将学生分数显示在单列中？
为此，请使用 UNION ALL。
我们首先创建一个表
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 命令在表中插入一些记录
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 语句从表中显示所有记录
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)
以下是对单列中显示学生分数的查询
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)
更新于: 22-Aug-2019
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