Database mysql statement final review CTGU

TRANSACTION Business

USE mydb;# Using a database 
DROP PROCEDURE IF EXITS mydb.proc_insert;# Ensure that stored procedures are writable （ only ）
DELIMITER $$ # Use $$ // And other symbols   Make a simple encapsulation of the whole short statement   delimiter （ Change the input terminator to $$  Double dollar sign ）
START TRANSCTION;# Open transaction 
INSERT INTO t_emp VALUES(1,'Nancy',301,2300);


## Insert statement 
commit;# Transaction submission 
END ##
DELIMITER;# tell mysql Interpreter , Whether the order has ended ,mysql Whether it can be carried out 

MYISAM

MyISAM yes MySQL The default database engine for （5.5 Prior to version ）, From the early ISAM Improved by . Although the performance is excellent , But there is one drawback ： Transaction not supported （transaction）. however , With the development of these years ,MySQL It also introduced InnoDB（ Another database engine ）, To strengthen reference integrity and concurrent violation processing mechanism , Then it gradually replaced MyISAM.

ISAM Index sequential access method （Index Sequential Access Mode）

InnoDB

InnoDB, yes MySQL One of the database engines of , Now is MySQL The default storage engine for , by MySQL AB Release binary One of the standards of .InnoDB from Innobase Oy The company developed ,2006 In May 2005, Oracle acquired . With the traditional ISAM And MyISAM comparison ,InnoDB The most important feature of the company is its support ACID Compatible transactions （Transaction） function , Be similar to PostgreSQL.

PostGreSQL

PostgreSQL It is an object of free software with very complete features - Relational database management system （ORDBMS）, It was developed by the computer department at the University of California POSTGRES,4.2 Version based object relational database management system .POSTGRES Many of our leading concepts only appeared later in the commercial website database .PostgreSQL Support most of SQL Standards and many other modern features , Such as complex queries 、 Foreign keys 、 trigger 、 View 、 Transaction integrity 、 Multi version concurrent control, etc . Again ,PostgreSQL It can also be extended in many ways , For example, by adding new data types 、 function 、 The operator 、 Aggregation function 、 Index method 、 Process language, etc . in addition , Because of the flexibility of the license , Anyone can use it for free for any purpose 、 Modify and distribute PostgreSQL.

concurrency control CONCURRENCY CONTROL

2.1 Table locks TABLE LOCK

LOCK TABLE student math=100 READ

2.2 Transaction isolation level TRANSACTION ISOLATION LEVEL

Dirty reading

It can't be read repeatedly

Fantasy reading

Fantasy reading Under the same conditions , The nonexistent data you have read , When you plug in , It is found that the data exists again , The point of it is insert. It can't be read repeatedly Under the same conditions , The data you read , Read it again and find that the value is different , The point is update and delete.
| Isolation level | Dirty reading | It can't be read repeatedly | Fantasy reading |
|–|–|–|
| | | |
Uncommitted read （Read uncommitted） Probably Probably Probably
Read committed （Read committed） impossible Probably Probably
Repeatable degrees （Repeatable read） impossible impossible Probably
Serializable （Serializable） impossible impossible impossible