First, the transaction
Second, the index
Third, rights management
Fourth, the three major paradigms
First, the transaction
Nature: either succeed together or fail together
Example: Transfer (must succeed at the same time, or both fail) if the power failure when the transfer did not turn out the money was gone, that's too bad.
Transaction principle: ACID
A (atomic): either succeed together or fail together (only two actions).
C (consistency): the integrity of the data before and after the transaction to be consistent, the total amount will not increase or decrease.
- No matter how many 100 who turn to, turn out and must own the remaining 100.
I (isolation): Hubuyingxiang data operations between multiple users.
- Isolate the problem caused when:
- Dirty read: A transaction reads data to another uncommitted transactions.
- Non-repeatable read: A transaction reads a row, data read many times inconsistent.
- Phantom read: a transaction reads another transaction to insert data, resulting in inconsistent before and after the reading.
D (persistent): depending on whether the transaction is committed to the implementation of the success or failure, irreversible after the transaction commits.
- When the transaction is successful, regardless of whether the power failure, restart the database after the money will not be restored to its original state (state after transfers).
- When a transaction fails, regardless of whether the power failure, restart the database after the money will be restored to its original state (the state before the transfer).
-- 创建数据库
create database if not exists changeMoney default character set 'utf8' default collate utf8_general_ci;
-- 创建表
create table shop(
`id` bigint(20) not null auto_increment,
`name` varchar(40) not null,
`money` decimal(40) not null,
primary key(`id`)
)engine = INNODB default charset=utf8;
-- 事务
-- 关闭自动提交
set autocommit = 0;
-- 开启事务
start transaction
update shop set money = money - 1000 where `name` = '张三';
update shop set money = money + 1000 where `name` = '李四';
--提交事务
commit;
--回滚（恢复到未开启事务时）
rollback;
-- (开启自动提交)
set autocommit = 1;
Transaction commit process:
Second, the index
Mysql help efficiently get the data structure of the data.
Index in a small amount of data is of little use when a large amount of data can be significantly increased query speed;
Index creation: create [Index] index index name (id_ table _ column name) on the table name (field name);
index:
-
Primary key index (primary key): a unique identifier, a table has only one primary key.
-
The only index (unique key): Avoid duplicate column appears, may be repeated multiple columns can be identified as a unique index.
-
General Index (key / index): default, can be set by key or index keywords.
-
Full-text indexing (FullText): Fast positioning data
influences:
-
After the index is created, query speed becomes faster, but slower insert and modify.
-
The more data in the table, create a slower index.
Index principle:
- Index not better.
- Do not indexed data to change frequently.
- Do not add a small amount of data indexing.
- Index generally applied to the fields used to query.
Recommended reading: https://blog.codinglabs.org/articles/theory-of-mysql-index.html
Third, rights management
1. Create a user
create user username identified by password;
2, change the current user password (MySQL8 failure)
set password = password (password);
3, modify the specified user password
set password for the username = password (password);
4, rename
rename user on a user name to the new user name;
5, full access to authorized users (authorized user can not give other authorized users)
. Grant all privileges on * * to username;
6, query authority
show grants for username;
Grants for root @ localhost Show; (query root privileges)
7, root user privileges
grant all privileges on *.* to ‘root@localhost’ with grants option;
8, revoke privileges
. Revoke all privileges on * * from user name;
9, delete user
drop user username;
Fourth, database backup
Backup reasons:
- Database to ensure data is not lost
- Data transfer
Backup way:
-
A physical copy: Go to the folder where the file mysql, copy the data files.
-
windows: the windows command line using mysqldump to export.
- Export: mysqldump -h host - u username -p password database [Table 1, Table 2, Table 3, ...]> drive: location or name.
-
Import:
- 1, log database, import tables need to import into the database.
- 2, source drive: / file. **
Fourth, the three major paradigms
First Normal Form (1NF):
Each column atomicity, table of only one thing.
Second Normal Form (2NF):
To meet the first paradigm, and each table only describe one thing.
Third Normal Form (3NF):
Each column of data satisfies the first and second paradigm, and to ensure that the primary key table and are directly related to, but not directly related.
Source: https://www.cnblogs.com/wsg25/p/9615100.html
Database design specifications:
Not more than three relational database table.
- Consider the commercial needs and goals (cost, user experience), database performance is more important.
- When the performance of regulatory issues, it is necessary to consider the appropriate normative.
- Some tables deliberately add some redundancy field, so that multi-table queries into a single-table queries.
- Deliberately increase the number of computed column (from large amounts of data into a small amount of data query: index)
