MySQL quick check
Because I often forget some mysql statements, keywords, operations, etc. in my daily work and study, I recently took some time to write the following content about mysql. It's like a dictionary
Reset mysql password
Data type
operator
Common functions
Data integrity
Basic operations of the database
Operations on the table itself Operations
on data in the table
Subquery
Multi-table connection
index
This article
preprocesses SQL statements
Custom functions and stored procedures
Programming in MySQL
view
Introduction
A view is a virtual table derived from one or more tables or other views through a select statement. No data is stored in the view. The data obtained from the view comes from the tables it references.
Table used by the example
mysql> create table people(id int primary key auto_increment,
name char(10) not null,
age int not null,sex enum('f','m'),sar float);
Query OK, 0 rows affected (0.02 sec)
mysql> desc people;
+-------+---------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------------+------+-----+---------+----------------+
| id | int | NO | PRI | NULL | auto_increment |
| name | char(10) | NO | | NULL | |
| age | int | NO | | NULL | |
| sex | enum('f','m') | YES | | NULL | |
| sar | float | YES | | NULL | |
+-------+---------------+------+-----+---------+----------------+
5 rows in set (0.01 sec)
Data from the table used
mysql> insert into people(name,age,sex,sar) values('铁子',23,'m',20000);
Query OK, 1 row affected (0.01 sec)
mysql> insert into people(name,age,sex,sar) values('潘子',18,'m',5000.4);
Query OK, 1 row affected (0.01 sec)
mysql> insert into people(name,age,sex,sar) values('嘎子',18,'m',5400.4);
Query OK, 1 row affected (0.01 sec)
mysql> insert into people(name,age,sex,sar) values('嘎叔',60,'m',15400.4);
Query OK, 1 row affected (0.01 sec)
mysql> insert into people(name,age,sex,sar) values('潘叔',60,'m',15450.8);
Query OK, 1 row affected (0.01 sec)
mysql> insert into people(name,age,sex,sar) values('老同志',69,'m',15450.8);
Query OK, 1 row affected (0.01 sec)
mysql> select * from people;
+----+-----------+-----+------+---------+
| id | name | age | sex | sar |
+----+-----------+-----+------+---------+
| 1 | 铁子 | 23 | m | 20000 |
| 2 | 潘子 | 18 | m | 5000.4 |
| 3 | 嘎子 | 18 | m | 5400.4 |
| 4 | 嘎叔 | 60 | m | 15400.4 |
| 5 | 潘叔 | 60 | m | 15450.8 |
| 6 | 老同志 | 69 | m | 15450.8 |
+----+-----------+-----+------+---------+
6 rows in set (0.00 sec)
Create view
CREATE
[OR REPLACE]
[ALGORITHM = {
UNDEFINED | MERGE | TEMPTABLE}]
[DEFINER = 用户]
[SQL SECURITY { DEFINER | INVOKER }]
VIEW 视图名 [(视图字段名,...)]
AS 查询语句
[WITH [CASCADED | LOCAL] CHECK OPTION]
- create view: Create a view, add or replace to replace the existing view
- algorithm: view algorithm:
- undefined: MySQL will automatically select the algorithm
- merge: merge the view definition and the view statement so that a certain part of the view definition replaces the corresponding part of the statement
- temptable: Store the view results in a temporary table, and then use the temporary table to execute statements
- definer: Definer, indicates the user who created the view, if not written, the default is the current user
- sql security: Specify who has permission to execute:
- definer: Execute with the permissions owned by the definer, default value
- invoker: Execute with the caller's permissions
- with check option: used to limit the insertion or update of rows in the table referenced by the view. If you use columns from other sources in a select statement, you must have select statement permissions. If there is or replace, you also need drop permissions.
- cascaded: The default value, which means that the conditions of all related views and tables must be met when updating the view.
- local: means that when updating the view, it only needs to meet the definition of the view itself.
# 创建一个视图将表people中年龄大于等于60的人
mysql> create or replace view v_old_people (姓名,年龄,性别)
as select name,age,sex from people where age >= 60;
Query OK, 0 rows affected (0.00 sec)
Delete view
DROP VIEW [IF EXISTS]
视图名 [, 视图名] ...
# 删除视图v_old_people
mysql> drop view v_old_people;
Query OK, 0 rows affected (0.01 sec)
Modify view
ALTER
[ALGORITHM = {
UNDEFINED | MERGE | TEMPTABLE}]
[DEFINER = user]
[SQL SECURITY { DEFINER | INVOKER }]
VIEW view_name [(column_list)]
AS select_statement
[WITH [CASCADED | LOCAL] CHECK OPTION]
Explanation Same as Create
ViewMore
view view
View definition
SHOW CREATE VIEW 视图名;
show table status like '视图名';
mysql> SHOW CREATE VIEW v_old_people;
+--------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+
| View | Create View | character_set_client | collation_connection |
+--------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+
| v_old_people | CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `v_old_people` (`姓名`,`年龄`,`性别`) AS select `people`.`name` AS `name`,`people`.`age` AS `age`,`people`.`sex` AS `sex` from `people` where (`people`.`age` >= 60) | utf8mb4 | utf8mb4_0900_ai_ci |
+--------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+
1 row in set (0.00 sec)
mysql> show table status like 'v_old_people';
+--------------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+-------------+------------+-----------+----------+----------------+---------+
| Name | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time | Update_time | Check_time | Collation | Checksum | Create_options | Comment |
+--------------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+-------------+------------+-----------+----------+----------------+---------+
| v_old_people | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | 2021-05-27 14:45:52 | NULL | NULL | NULL | NULL | NULL | VIEW |
+--------------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+-------------+------------+-----------+----------+----------------+---------+
1 row in set (0.00 sec)
View data
select 字段名[,...] from 视图名;
mysql> select * from v_old_people;
+-----------+--------+--------+
| 姓名 | 年龄 | 性别 |
+-----------+--------+--------+
| 嘎叔 | 60 | m |
| 潘叔 | 60 | m |
| 老同志 | 69 | m |
+-----------+--------+--------+
3 rows in set (0.00 sec)