视图就是存储下来的SELECT语句，没有存任何其他内容，是基于某些基表的查询结果。一般情况不允许往视图中插入数据
视图是一个虚表，视图所依赖的表称之为基表
创建视图
CREATE VIEW
查看帮助：
mysql> help create view Name: 'CREATE VIEW' Description: Syntax: CREATE [OR REPLACE] [ALGORITHM = {UNDEFINED | MERGE | TEMPTABLE}] [DEFINER = { user | CURRENT_USER }] [SQL SECURITY { DEFINER | INVOKER }] VIEW view_name [(column_list)] AS select_statement [WITH [CASCADED | LOCAL] CHECK OPTION]
1，创建一个视图，用来存放查询students所有信息
mysql> CREATE VIEW students_view AS SELECT * FROM students; Query OK, 0 rows affected (0.36 sec) //可以看到创建视图成功后，tables里面多了一个表(就是创建的视图) mysql> show databases; +--------------------+ | Database | +--------------------+ | information_schema | | classes | | fsx | | mysql | | performance_schema | | students | | test | +--------------------+ 7 rows in set (0.00 sec) //不同于真正的表，可以查看该视图的具体信息 mysql> SELECT * FROM students_view ; +-----+--------+-----+------+------+------+------+---------------------+ | sid | name | age | sex | cid1 | cid2 | tid | create_time | +-----+--------+-----+------+------+------+------+---------------------+ | 1 | tony | 18 | BOY | 2 | 4 | 3 | 2018-05-15 12:09:28 | | 2 | Cindy | 21 | GRIL | 3 | 6 | NULL | 2018-05-15 12:15:30 | | 3 | Alice | 19 | GRIL | 1 | NULL | NULL | 2018-05-15 13:11:37 | | 4 | Kobe | 25 | BOY | 11 | 1 | 2 | 2018-05-15 13:18:52 | | 5 | Tom | 19 | BOY | 4 | 3 | 7 | 2018-05-15 13:12:21 | | 6 | fsx | 24 | BOY | 1 | 3 | 9 | 2018-05-15 13:13:05 | | 7 | Qpy | 21 | GRIL | 3 | 1 | NULL | 2018-05-15 12:15:37 | | 8 | Coco | 27 | GRIL | 6 | 2 | 8 | 2018-05-15 12:15:38 | | 9 | Bob | 20 | BOY | 2 | 1 | NULL | 2018-05-15 12:15:53 | | 10 | Liming | 22 | BOY | 6 | 3 | 2 | 2018-05-15 12:13:28 | +-----+--------+-----+------+------+------+------+---------------------+ 10 rows in set (0.00 sec) /使用SHOW TABLE STATUS\G找到studetns_view表的信息 mysql> SHOW TABLE STATUS\G *************************** 3. row *************************** Name: students_view Engine: NULL Version: NULL Row_format: NULL Rows: NULL Avg_row_length: NULL Data_length: NULL Max_data_length: NULL Index_length: NULL Data_free: NULL Auto_increment: NULL Create_time: NULL Update_time: NULL Check_time: NULL Collation: NULL Checksum: NULL Create_options: NULL Comment: VIEW mysql> DESC students_view; +-------------+---------------------+------+-----+---------------------+-------+ | Field | Type | Null | Key | Default | Extra | +-------------+---------------------+------+-----+---------------------+-------+ | sid | tinyint(3) unsigned | NO | | 0 | | | name | varchar(30) | NO | | NULL | | | age | tinyint(4) | NO | | NULL | | | sex | enum('BOY','GRIL') | YES | | NULL | | | cid1 | tinyint(4) | YES | | NULL | | | cid2 | tinyint(4) | YES | | NULL | | | tid | tinyint(4) | YES | | NULL | | | create_time | timestamp | NO | | 0000-00-00 00:00:00 | | +-------------+---------------------+------+-----+---------------------+-------+ 8 rows in set (0.00 sec)
当我们创建好一个关于students表的VIEW后，下次想要查询students信息就直接使用VIEW，更加方便
mysql> SELECT name,cid1 FROM students_view; +--------+------+ | name | cid1 | +--------+------+ | tony | 2 | | Cindy | 3 | | Alice | 1 | | Kobe | 11 | | Tom | 4 | | fsx | 1 | | Qpy | 3 | | Coco | 6 | | Bob | 2 | | Liming | 6 | +--------+------+ 10 rows in set (0.00 sec)
注意：不违反基表的存储法则，是可以向视图中插入数据的，但是一般很难不违反基表的存储法则。通常情况下，我们使用视图只是作为一个查找的虚表，并不是为了插入数据。所以，尽量不要想着给视图插入数据的操作。
删除视图
查看删除视图的帮助：
mysql> HELP DROP VIEW Name: 'DROP VIEW' Description: Syntax: DROP VIEW [IF EXISTS] view_name [, view_name] ... [RESTRICT | CASCADE]
1，删除students_view视图
mysql> DROP VIEW students_view; Query OK, 0 rows affected (0.00 sec) mysql> SHOW TABLES; +-------------------+ | Tables_in_classes | +-------------------+ | courses | | students | | subjects | | teachers | +-------------------+ 4 rows in set (0.00 sec)
基于视图查询，是没有索引的，读取速度不叫慢，所以一般情况不建议使用视图，只有在一些特殊情况下使用(跟安全相关)。
有些数据支持雾化视图，即可以将查询的结果保存下来。这样再次查询的时候，就不用去执行目表中的查询操作，一次查询即可。但是也有新的问题：如果母表更新了，使用雾化视图时就会得不到最新数据。所以在更新不频繁的表上使用雾化视图更好。
使用SHOW CREATE VIEW view_name可以查看创建的视图的具体过程、映射关系和字符集、排序规则信息
mysql> SHOW CREATE VIEW stu_view\G *************************** 1. row *************************** View: stu_view Create View: CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `stu_view` AS select `students`.`sid` AS `sid`,`students`.`name` AS `name`,`students`.`age` AS `age`,`students`.`sex` AS `sex`,`students`.`cid1` AS `cid1`,`students`.`cid2` AS `cid2`,`students`.`tid` AS `tid`,`students`.`create_time` AS `create_time` from `students` character_set_client: utf8 collation_connection: utf8_general_ci 1 row in set (0.00 sec) mysql> SHOW CREATE VIEW stu_view; +----------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+ | View | Create View | character_set_client | collation_connection | +----------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+ | stu_view | CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `stu_view` AS select `students`.`sid` AS `sid`,`students`.`name` AS `name`,`students`.`age` AS `age`,`students`.`sex` AS `sex`,`students`.`cid1` AS `cid1`,`students`.`cid2` AS `cid2`,`students`.`tid` AS `tid`,`students`.`create_time` AS `create_time` from `students` | utf8 | utf8_general_ci | +----------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+ 1 row in set (0.00 sec) //同理使用SHOW命令也可以查看如何创建的表、库、索引等 mysql> SHOW CREATE TABLE tearchers; ERROR 1146 (42S02): Table 'classes.tearchers' doesn't exist mysql> SHOW CREATE TABLE teachers; +----------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Table | Create Table | +----------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | teachers | CREATE TABLE `teachers` ( `tid` tinyint(3) unsigned NOT NULL AUTO_INCREMENT, `tname` varchar(30) NOT NULL, `age` tinyint(3) unsigned NOT NULL, PRIMARY KEY (`tid`) ) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=gbk | +----------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1 row in set (0.00 sec)
mysql命令中的-e选项
mysql命令选项-e，可以在非mysql交互模式下实现对数据库的管理
[root@mysql ~]# mysql -e 'CREATE DATABASE edb;' [root@mysql ~]# mysql -e 'SHOW DATABASES;' +--------------------+ | Database | +--------------------+ | information_schema | | classes | | edb | | fsx | | mysql | | performance_schema | | students | | test | +--------------------+
脚本批插入数据
1，写一个脚本实现对students插入几组数据
[root@mysql ~]# mysql -e 'SELECT * FROM classes.students;' +-----+--------+-----+------+------+------+------+---------------------+ | sid | name | age | sex | cid1 | cid2 | tid | create_time | +-----+--------+-----+------+------+------+------+---------------------+ | 1 | tony | 18 | BOY | 2 | 4 | 3 | 2018-05-15 12:09:28 | | 2 | Cindy | 21 | GRIL | 3 | 6 | NULL | 2018-05-15 12:15:30 | | 3 | Alice | 19 | GRIL | 1 | NULL | NULL | 2018-05-15 13:11:37 | | 4 | Kobe | 25 | BOY | 11 | 1 | 2 | 2018-05-15 13:18:52 | | 5 | Tom | 19 | BOY | 4 | 3 | 7 | 2018-05-15 13:12:21 | | 6 | fsx | 24 | BOY | 1 | 3 | 9 | 2018-05-15 13:13:05 | | 7 | Qpy | 21 | GRIL | 3 | 1 | NULL | 2018-05-15 12:15:37 | | 8 | Coco | 27 | GRIL | 6 | 2 | 8 | 2018-05-15 12:15:38 | | 9 | Bob | 20 | BOY | 2 | 1 | NULL | 2018-05-15 12:15:53 | | 10 | Liming | 22 | BOY | 6 | 3 | 2 | 2018-05-15 12:13:28 | +-----+--------+-----+------+------+------+------+---------------------+
先在终端常是一次添加一行数据：
[root@mysql ~]# mysql -e "INSERT INTO classes.students (name,age,sex,cid1,cid2,tid) VALUES('james',25,'BOY',3,2,2);" [root@mysql ~]# mysql -e "SELECT * FROM classes.students;" +-----+--------+-----+------+------+------+------+---------------------+ | sid | name | age | sex | cid1 | cid2 | tid | create_time | +-----+--------+-----+------+------+------+------+---------------------+ | 1 | tony | 18 | BOY | 2 | 4 | 3 | 2018-05-15 12:09:28 | | 2 | Cindy | 21 | GRIL | 3 | 6 | NULL | 2018-05-15 12:15:30 | | 3 | Alice | 19 | GRIL | 1 | NULL | NULL | 2018-05-15 13:11:37 | | 4 | Kobe | 25 | BOY | 11 | 1 | 2 | 2018-05-15 13:18:52 | | 5 | Tom | 19 | BOY | 4 | 3 | 7 | 2018-05-15 13:12:21 | | 6 | fsx | 24 | BOY | 1 | 3 | 9 | 2018-05-15 13:13:05 | | 7 | Qpy | 21 | GRIL | 3 | 1 | NULL | 2018-05-15 12:15:37 | | 8 | Coco | 27 | GRIL | 6 | 2 | 8 | 2018-05-15 12:15:38 | | 9 | Bob | 20 | BOY | 2 | 1 | NULL | 2018-05-15 12:15:53 | | 10 | Liming | 22 | BOY | 6 | 3 | 2 | 2018-05-15 12:13:28 | | 11 | james | 25 | BOY | 3 | 2 | 2 | 2018-05-16 09:36:16 | +-----+--------+-----+------+------+------+------+---------------------+
编写脚本mysql_test.sh
在编写前创建一个test2的表
mysql> create TABLE test2(sid TINYINT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,name VARCHAR(30) NOT NULL,age TINYINT NOT NULL,sex ENUM('girl','boy'),cid1 TINYINT NOT NULL,cid2 TINYINT NOT NULL,tid TINYINT NOT NULL,time TIMESTAMP); Query OK, 0 rows affected (0.16 sec)
#/bin/bash while [ 1 ] do ##生成随机姓名## name='' for i in {1..3} do name=$name$(tr -dc a-z < /dev/urandom | head -c1) done #### age=$(shuf -i 16-28 -n 1) cid1=$(shuf -i 1-10 -n 1) cid2=$(shuf -i 1-10 -n 1) tid=$(shuf -i 1-5 -n 1) ##性别随机生成## pool=(1 2) num=${#pool[*]} sex=${pool[$((RANDOM%num))]} case $sex in 1) sex="girl";; 2) sex="boy";; esac #### `mysql -e "INSERT INTO classes.test2 (name,age,sex,cid1,cid2,tid) VALUES('$name',$age,'$sex',$cid1,$cid2,$tid)"` done
执行完脚本后，查看数据库test2表中内容
mysql> SELECT * FROM test2; +-----+------+-----+------+------+------+-----+---------------------+ | sid | name | age | sex | cid1 | cid2 | tid | time | +-----+------+-----+------+------+------+-----+---------------------+ | 1 | vxt | 22 | boy | 1 | 2 | 3 | 2018-05-16 10:50:02 | | 2 | hly | 21 | boy | 9 | 8 | 5 | 2018-05-16 10:50:02 | | 3 | kew | 17 | boy | 3 | 10 | 4 | 2018-05-16 10:50:03 | | 4 | tnz | 25 | girl | 10 | 5 | 5 | 2018-05-16 10:50:03 | | 5 | imh | 16 | girl | 9 | 4 | 2 | 2018-05-16 10:50:03 | | 6 | fdu | 25 | boy | 1 | 9 | 4 | 2018-05-16 10:50:03 | | 7 | fro | 21 | girl | 9 | 10 | 3 | 2018-05-16 10:50:03 | | 8 | ykf | 27 | girl | 4 | 5 | 1 | 2018-05-16 10:50:03 | | 9 | gff | 26 | girl | 9 | 2 | 5 | 2018-05-16 10:50:03 | | 10 | fwx | 16 | boy | 3 | 7 | 1 | 2018-05-16 10:50:03 | | 11 | vus | 24 | girl | 8 | 9 | 1 | 2018-05-16 10:50:03 | | 12 | tac | 20 | boy | 4 | 6 | 3 | 2018-05-16 10:50:03 | | 13 | dev | 21 | boy | 5 | 6 | 2 | 2018-05-16 10:50:04 | | 14 | nfu | 24 | boy | 6 | 8 | 3 | 2018-05-16 10:50:04 | | 15 | akf | 24 | girl | 1 | 2 | 3 | 2018-05-16 10:50:04 | | 16 | wsk | 24 | boy | 3 | 6 | 4 | 2018-05-16 10:50:04 | | 17 | wih | 25 | boy | 1 | 6 | 5 | 2018-05-16 10:50:04 | | 18 | cif | 18 | boy | 5 | 2 | 2 | 2018-05-16 10:50:04 | | 19 | avj | 18 | boy | 7 | 2 | 4 | 2018-05-16 10:50:04 | | 20 | akh | 25 | girl | 2 | 1 | 2 | 2018-05-16 10:50:04 | | 21 | zdf | 22 | girl | 1 | 1 | 5 | 2018-05-16 10:50:04 | | 22 | uzc | 28 | boy | 2 | 3 | 3 | 2018-05-16 10:50:04 | //由于PRIMARY KEY值最大到255所以这个只能创建255个行数据