Mysql 索引、视图

# 给 name 字段创建索引 aa
mysql> create index aa on t_student(name);

# 查看索引
mysql> show index from t_student;

+-----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table     | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+-----------+------------+----------+--------------+-------------+-----------+---
| t_student |          1 | aa       |            1 | name        | A         |           2 |     NULL | NULL   | YES  | BTREE      |         |
+-----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+

# 删除索引 aa
mysql> drop index aa on t_student;

# 给 name 字段创建唯一索引
mysql> create unique index bb on t_student(name);

mysql> show index from t_student;

+-----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table     | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+-----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| t_student |          0 | bb       |            1 | name        | A         |           2 |     NULL | NULL   | YES  | BTREE      |         |
+-----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+

# 给 score 字段添加主键索引
mysql> alter table t_course add primary key(score);

mysql> show index from t_course;

+----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table    | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| t_course |          0 | PRIMARY  |            1 | score       | A         |           6 |     NULL | NULL   |      | BTREE      |         |
+----------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+

# 创建视图 v_stu
mysql> create view v_stu as (select id,name,age from t_student);

# 查看创建的视图 v_stu
mysql> show tables;

+-------------------+
| Tables_in_student |
+-------------------+
| t_course          |
| t_student         |
| v_stu             |
+-------------------+

mysql> select * from v_stu;
+----+----------+------+
| id | name     | age  |
+----+----------+------+
|  1 | zhangsan |   18 |
|  2 | wangwu   |   20 |
|  3 | zhaoliu  |   19 |
|  4 | lisi     |   22 |
+----+----------+------+

mysql> alter view v_stu as (select id,name from t_student);

mysql> select * from v_stu;
+----+----------+
| id | name     |
+----+----------+
|  4 | lisi     |
|  2 | wangwu   |
|  1 | zhangsan |
|  3 | zhaoliu  |
+----+----------+

# 删除视图 v_cou
mysql> drop view v_cou;

mysql> show tables;
+-------------------+
| Tables_in_student |
+-------------------+
| t_course          |
| t_student         |
| v_stu             |
+-------------------+