mysql索引与视图_MySQL

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原始表student字段：

mysql> select column_name,data_type    -> from information_schema.columns    -> where table_name = 'student';+-------------+-----------+| column_name | data_type |+-------------+-----------+| stu_id      | int       || stu_name    | varchar   || stu_tel     | int       || stu_score   | int       |+-------------+-----------+4 rows in set (0.01 sec)

表中原始数据：

mysql> select * from student;+--------+----------+---------+-----------+| stu_id | stu_name | stu_tel | stu_score |+--------+----------+---------+-----------+|      1 | a        |     151 |        60 ||      2 | b        |     152 |        61 ||      3 | c        |     153 |        62 ||      4 | d        |     154 |        63 |+--------+----------+---------+-----------+4 rows in set (0.00 sec)

索引创建格式：

create [ <index type> ] index <index name> [ using {btree | hash} ] on table specification ( <column in index> [,<column in index> ] )<index type> := unique | fulltext | spatial<column in index>:=<column name> [asc | desc]

创建一个最简单的索引：

mysql> create index stu_index     -> on student(stu_id);Query OK, 0 rows affected (0.36 sec)Records: 0  Duplicates: 0  Warnings: 0

这里创建立一个非唯一性的索引，其中默认使用asc升序排列。

如果没有指定using声明的话，mysql自动创建一个B树。所以上面的索引其实是这样子的：

mysql> create index stu_index using btree     -> on student(stu_id asc);Query OK, 0 rows affected (0.19 sec)Records: 0  Duplicates: 0  Warnings: 0

当然，btree索引可以换成哈希索引。

也可以为多个列创建唯一的索引：

mysql> create unique index stu_index using hash     -> on student(stu_id,stu_name);Query OK, 0 rows affected (0.19 sec)Records: 0  Duplicates: 0  Warnings: 0

添加索引：

mysql> alter table student    -> add unique index stu_index2    -> using hash (stu_tel);Query OK, 0 rows affected (0.36 sec)Records: 0  Duplicates: 0  Warnings: 0

删除索引：

mysql> drop index stu_index on student;Query OK, 0 rows affected (0.22 sec)Records: 0  Duplicates: 0  Warnings: 0

创建表时定义索引：

mysql> create table student(    -> stu_id          int primary key,    -> stu_name        varchar(5) not null,    -> stu_tel         int(5) unique,    -> stu_score       int(2),    -> index stu_index(stu_id)    -> );

只需在表的最后添加创建索引的语句即可。

视图是数据库中的虚拟表，它存储的不是自己的内容，而是经过select从其他表整合而来的。当其他表的内容改变是，视图内的内容跟着改变。在一定条件下，对视图的更新也将改变源表。

创建视图：

create [ or replace ] view <view name> [<column list>] as <table expression> [with [ cascaded |local ] check option ]mysql> create view view1 as    -> (select * from student);Query OK, 0 rows affected (0.16 sec)

mysql> select * from view1;+--------+----------+---------+-----------+| stu_id | stu_name | stu_tel | stu_score |+--------+----------+---------+-----------+|      1 | a        |     151 |        60 ||      2 | b        |     152 |        61 ||      3 | c        |     153 |        62 ||      4 | d        |     154 |        63 |+--------+----------+---------+-----------+4 rows in set (0.00 sec)

创建视图时，如果视图已存在，可用replace重新覆盖创建。

创建视图时还可以更改原始列名。

mysql> create or replace view view1(id,name,tel,score) as    -> (select * from student);Query OK, 0 rows affected (0.03 sec)

mysql> select * from view1;+----+------+------+-------+| id | name | tel  | score |+----+------+------+-------+|  1 | a    |  151 |    60 ||  2 | b    |  152 |    61 ||  3 | c    |  153 |    62 ||  4 | d    |  154 |    63 |+----+------+------+-------+4 rows in set (0.00 sec)

当一个视图可以更新时，就能够使用[with [ cascaded |local ] check option ]选项对更新对有效检查。

删除视图：

drop view view1;

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