Transactions, views, triggers, stored engine, backup

[TOC]

First, the transaction

1. What matters

• A transaction is concurrency control units, refers to a set of operations are executed either succeed or both fail.

2. What is the use affairs

• Ensure the integrity of the database data.

3. Use

• grammar:

  start transaction;
    sql语句
  commit/rollback;
  # commit 的意思是上面的处理都正确，现在提交，修改本地数据
  # rollback 的意思是上面的处理有错误或者问题，取消上面所有的操作，回到start transaction 之前的状态
  
  

4. Features transaction (the ACID)

(1) atom of (Atomicity)

• A transaction is a logical unit of work database, all operations in the transaction included either do or do not do

(2) Consistency (Consistency)

• After the transaction occurs and former refers to the occurrence, the total data still matches

(3) isolation (Isolation)

• Execution of a transaction can not interfere with other transactions. I.e., operation and use of the data inside a transaction other concurrent transactions are isolated and can not interfere with each other concurrently executing transactions between the various

(4) persistent (Durability)

• Refers to a transaction once submitted, change the data in a database it should be permanent

Two, MySQL storage engine

1. InnoDB

• High-performance, support services, support row lock
• MySQL5.0 version and above is the default storage engine

2. MyIsam

• Low performance, does not support transactions, supports table locks
• Now also gradually eliminated

Three View

1. What is the view

• A view is a virtual table (non-real), it is to obtain a dynamic data set based on a SQL statement, and name it. After using the name you can get the result set, and the result set can be used as a table

• However, the view will increase the burden on the database system, now basically no one to use.

2. Use the view

• #增加视图：
    		create view 视图名 as SQL语句;
  
  #删除：	
    		drop view v1;
  
  #查看视图：
    		select * from 视图名;
  

Fourth, the flip-flop

1. What is the trigger

• A trigger is a grammar. Its function is to associate multiple SQL statements together, when we execute the specified SQL statement will execute other SQL statements simultaneously.

2. The use of triggers

• 两张表：
    		订单表     库存表
  
    	场景：
    		当我下一个订单的时候， 订单表中需要增加一个记录， 同时库存表中需要减1
    		这两个操作是同时发生的，  并且前一个操作出发后一个操作
  
  # 使用方法：
    		# 例子：当向tb1表中添加一条数据的同时， 向tb2表添加一条数据
    		增加：
    			delimiter //
  
    			CREATE TRIGGER 触发器名
                  BEFORE INSERT ON t2 FOR EACH ROW #触发条件
    			BEGIN
    				INSERT INTO t3 (NAME) VALUES ('aa'); # 触发后执行的sql语句
    			END //
  
    			delimiter ;  
  
  #删除：
  drop trigger 触发器名；    
  
  # 查看
  
  show triggers\G
  

V. Stored Procedures

1. What is a stored procedure

• That is a function of the database system, SQL statements thrown into a pile of stored procedure, and then to call a stored procedure by this name inside the actuator in python similar functions, stored procedures, SQL statements.

2. The use of stored procedures

• #创建：
  
    		delimiter //
  
    		create procedure 存储过程名()
    		BEGIN
    			select * from user where id=2; # SQL语句
    		END //
  
    		delimiter ;
  
  # 调用存储过程：
    		call 存储过程名();
  
  # 删除：    
    		drop procedure 存储过程名;
  

Six built-in functions (common)

CHAR_LENGTH(str)
			返回值为字符串str 的长度，长度的单位为字符。一个多字节字符算作一个单字符。
			对于一个包含五个二字节字符集, LENGTH()返回值为 10, 而CHAR_LENGTH()的返回值为5。
		
		CONCAT(str1,str2,...)
			字符串拼接
			如有任何一个参数为NULL ，则返回值为 NULL。
		FORMAT(X,D)
			将数字X 的格式写为'#,###,###.##',以四舍五入的方式保留小数点后 D 位， 并将结果以字符串的形式返回。若  D 为 0, 则返回结果不带有小数点，或不含小数部分。
			例如：
				SELECT FORMAT(12332.1,4); 结果为： '12,332.1000'
		INSTR(str,substr)
			返回字符串 str 中子字符串的第一个出现位置。
		LEFT(str,len)
			返回字符串str 从开始的len位置的子序列字符。
		LOWER(str)
			变小写
		UPPER(str)
			变大写
		LTRIM(str)
			返回字符串 str ，其引导空格字符被删除。
		RTRIM(str)
			返回字符串 str ，结尾空格字符被删去。
		SUBSTRING(str,pos,len)
			获取字符串子序列
		LOCATE(substr,str,pos)
			获取子序列索引位置
		REPEAT(str,count)
			返回一个由重复的字符串str 组成的字符串，字符串str的数目等于count 。
			若 count <= 0,则返回一个空字符串。
			若str 或 count 为 NULL，则返回 NULL 。
		REPLACE(str,from_str,to_str)
			返回字符串str 以及所有被字符串to_str替代的字符串from_str 。
		REVERSE(str)
			返回字符串 str ，顺序和字符顺序相反。
		RIGHT(str,len)
			从字符串str 开始，返回从后边开始len个字符组成的子序列

Seven, database backup

1. Why should data be backed up

• A large number of value-added data, for unexpected accidents result in loss of data, so to back it up

2. How to back up

用法：
				#语法：
				# mysqldump -h 服务器 -u用户名 -p密码 数据库名 表名,  表名,.... > 备份文件的路径（如：aaa.sql  ， 这个是相对路径，也可以填绝对路径，都要以 .sql 格式结尾。） 

				#示例：
				#单库备份
				mysqldump -uroot -p123 db1 > db1.sql
				mysqldump -uroot -p123 db1 table1 table2 > db1-table1-table2.sql

				#多库备份
				mysqldump -uroot -p123 --databases db1 db2 mysql db3 > db1_db2_mysql_db3.sql

				#备份所有库
				mysqldump -uroot -p123 --all-databases > all.sql
		
			重新导入：
				mysql> source D:/test3.sql;