MYSQL数据库--索引、视图练习
创建完表的结果如下
mysql> desc Course;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| Cno | int | NO | PRI | NULL | |
| Cname | varchar(20) | NO | | NULL | |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.01 sec)mysql> desc Sc;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| Sno | int | NO | | NULL | |
| Cno | varchar(10) | NO | PRI | NULL | |
| Score | int | NO | | NULL | |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)mysql> desc Student;
+-------+-------------+------+-----+-----------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+-----------+----------------+
| Sno | int | NO | PRI | NULL | auto_increment |
| Sname | varchar(30) | NO | UNI | NULL | |
| Ssex | varchar(2) | NO | | NULL | |
| Sage | int | NO | | NULL | |
| Sdept | varchar(10) | NO | | 计算机 | |
+-------+-------------+------+-----+-----------+----------------+
5 rows in set (0.01 sec)1.修改Student表中年龄（sage）字段属性，数据类型由int 改变为smallint
mysql> alter table Student modify Sage smallint;
Query OK, 0 rows affected (0.04 sec)
Records: 0 Duplicates: 0 Warnings: 0mysql> desc Student;
+-------+-------------+------+-----+-----------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+-----------+----------------+
| Sno | int | NO | PRI | NULL | auto_increment |
| Sname | varchar(30) | NO | UNI | NULL | |
| Ssex | varchar(2) | NO | | NULL | |
| Sage | smallint | YES | | NULL | |
| Sdept | varchar(10) | NO | | 计算机 | |
+-------+-------------+------+-----+-----------+----------------+
5 rows in set (0.00 sec)
2.为Course表中Cno课程号字段设置索引，并查看索引
mysql> create index Course_Cno on Course(Cno);
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0mysql> show index from Course;
+--------+------------+------------+--------------+-------------+-----------+----- --------+----------+--------+------+------------+---------+---------------+------- --+------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Card inality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | Visibl e | Expression |
+--------+------------+------------+--------------+-------------+-----------+----- --------+----------+--------+------+------------+---------+---------------+------- --+------------+
| Course | 0 | PRIMARY | 1 | Cno | A | 0 | NULL | NULL | | BTREE | | | YES | NULL |
| Course | 1 | Course_Cno | 1 | Cno | A | 0 | NULL | NULL | | BTREE | | | YES | NULL |
+--------+------------+------------+--------------+-------------+-----------+----- --------+----------+--------+------+------------+---------+---------------+------- --+------------+
2 rows in set (0.01 sec)
3.为SC表建立按学号（sno）和课程号（cno）组合的升序得到主键索引，索引名为SC_INDEDX
mysql> create unique index Sc_index on Sc(Sno asc,Cno asc);
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0mysql> show index from Sc\G
*************************** 1. row ***************************Table: ScNon_unique: 0Key_name: PRIMARYSeq_in_index: 1Column_name: CnoCollation: ACardinality: 0Sub_part: NULLPacked: NULLNull:Index_type: BTREEComment:
Index_comment:Visible: YESExpression: NULL
*************************** 2. row ***************************Table: ScNon_unique: 0Key_name: Sc_indexSeq_in_index: 1Column_name: SnoCollation: ACardinality: 0Sub_part: NULLPacked: NULLNull:Index_type: BTREEComment:
Index_comment:Visible: YESExpression: NULL
*************************** 3. row ***************************Table: ScNon_unique: 0Key_name: Sc_indexSeq_in_index: 2Column_name: CnoCollation: ACardinality: 0Sub_part: NULLPacked: NULLNull:Index_type: BTREEComment:
Index_comment:Visible: YESExpression: NULL
3 rows in set (0.01 sec)
4创建一视图stu_info，查询全体学生的姓名，性别，课程号，成绩
mysql> create view stu_info as select Sname '姓名',Ssex '性别',Cname '课程名',Scor e '成绩' from Student join Sc on Student.Sno=Sc.sno join Course on Sc.Cno=Course. Cno;
5.删除所有索引
mysql> drop index Sc_index on Sc;
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0mysql> drop index Course_Cno on Course;
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0