【MySQL】Basic operations such as adding, deleting, modifying, checking, backup, and restoration of the database

1. Create a database—create

CREATE DATABASE [IF NOT EXISTS] db_name [create_specification [,
create_specification] ...]
create_specification:
[DEFAULT] CHARACTER SET charset_name
[DEFAULT] COLLATE collation_name

• capitalized keywords
• [] is optional
• CHARACTER SET: Specifies the character set used by the database
• COLLATE: Specifies the validation rules for the database character set

1.1 Character set and verification rules

When creating a database, there are two code sets:
1. Database code set - the database will store data in the future

2. Database verification set——supports the encoding used by the database for field comparison, and is essentially an encoding format used to read data in the database

No matter what operation is performed on the data, the database must ensure that the operation and encoding must match to prevent garbled characters

1.1.1 View the system default character set and verification rules

show variables like 'character_set_database';//查看默认字符集
show variables like 'collation_database';//查看默认校验规则

show charset; View the character set supported by the database
show collation; View the character set verification rules supported by the database

1.1.2 Create database by default

if not exists: Create if it does not exist, and return warning if it exists

1.1.3 Specify code set to build database

key statement

charset=utf8/设置字符集*/ collate utf8_general_ci/*设置校验规则*/

1.2 The essence of database construction

In the previous article,show databases it was said that the essence of a database is a directory, so it can be found by directly creating a directory under the specified folder , but it is not recommended to do so

2. View the database and its related properties—show

2.1 Display all databases

As mentioned earlier, show databasesdisplay all databases under mysql

2.2 Display the database creation statement

show create database 数据库名；

/ ... / is not a comment, he said that if the mysql version is greater than 4.01, the d2 creation statement becomes

CREATE DATABASEd2 DEFAULT CHARACTER SET utf8 COLLATE utf8_bin;

3.2 Display the current database

select database();

3. Modify the database—alter

ALTER DATABASE db_name
[alter_spacification [,alter_spacification]...]
alter_spacification:
[DEFAULT] CHARACTER SET charset_name
[DEFAULT] COLLATE collation_name

The modification of the database mainly refers to modifying the character set of the database, and the verification rules

As shown in the figure below, the original check code of database d2 is utf8_bin, and its check code is changed to utf8 by ALTER

4. Database deletion—drop

If the database exists, delete it

DROP DATABASE [IF EXISTS] db_ name;

The result after performing the delete:

1. The corresponding database cannot be seen inside the database
2. The corresponding database folder is deleted, cascaded deletion, and all the data tables in it are deleted

Note: Don't delete the database at will, otherwise you will become a man who gets 600,000 in 3 months

V. Supplement: The impact of verification rules on the database

What is the role of the aforementioned encoding set in the database? Take a look at a case

Create a database with validation rules using utf8_ general_ ci [case insensitive]

Case-sensitive queries and results [utf8_bin]

6. Database backup and restoration (the most important)

6.1 Backup and restore of database

As mentioned earlier, the essence of the database is the file directory under Linux. The easiest way is to copy that directory directly, but this method is not very portable. Let me introduce the commonly used backup methods

mysqldump -P3306 -u root -p 密码 -B 数据库名 > 数据库备份存储的文件路径

Step 1: Back up the database.

Not only the data in the database is backed up in the sql file, but also the previous effective operations are also backed up.

Step 2: Delete the database

Step Three: Restoring the Database

6.2 Other situations

6.2.1 Backup table only

mysqldump -u root -p 数据库名 表名1 表名2 > D:/mytest.sql

6.2.2 Backing up multiple databases

mysqldump -u root -p -B 数据库名1 数据库名2 ... > 数据库存放路径

6.2.3 -B option

If the -B parameter is not included when backing up a database, when restoring the database, you need to create an empty database first, then use (use db_name) the database, and then use source to restore