mysql索引与视图

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mysql索引与视图

来源: 作者: 时间:2016-01-30 09:02 【

原始表student字段:mysql select column_name,data_type - from information_schema columns - where table_name = student ;+-------------+-----------+| column_name |

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 ]
> 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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