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This article mainly introduces the relevant knowledge of "what are the basic operations of MySQL". The editor shows you the operation process through actual cases, and the operation method is simple, fast and practical. I hope this article "what are the basic operations of MySQL" can help you solve the problem.

1. Operation of the library

Check which libraries are available by default under the current mysql database

Show databases

Create a library create database database_name

Create database test11

Naming conventions for database_name library names:

(1) consists of letters, numbers, underscores, @, # and

(2) the initials cannot be numbers and $

(3) cannot be the keyword of mysql database

(4) spaces and special characters are not allowed

(5) length is less than 128 bits

Use a library

Use database_name

Check which library is currently being used / connected

Elect database ()

View all the tables under the current library

Show tables

Delete a library

Drop database database_name;2. Operation of the table

The table is a very important object in the mysql database, and it is the basic element of the database. The table is composed according to the format of rows and columns, which is mainly used to store data.

Example: storing data in tabular form

Student number, name, age, grade.

1 Zhang San 30 100

2 Li Si 25 90

Create a tabl

Syntax:

Create table table_name (column name 1 data type, column name 2 data type, column name 3 data type, column name 4 data type,.... Column name n data type); create table mytest (id int, name varchar (20), age int, birthday date); select * from mytest

Data type:

Integer int (digits)

Decimal type / floating point type double

String type varchar (digits) becomes longer

Char (digits) fixed length

Varchar (5) Zhang San

Char (5) Zhang San xxx

"Zhang San"

Date type date

Create a company library company

Create database company

Use the company library

Use company

Create a department table t_dept department number, department name, address

Create table t_dept (deptno int, dname varchar (20), loc varchar (20)); view table structure

View the structure of the table

Desc table_name

View table definition in detail

Show create table table_name;desc tweets show create table t_dept\ G; (instead of\ G; can make the display result more beautiful) delete the table

Delete a table

Drop table table_name;drop table tweedept; `modify the table

① modifies the table name

Syntax:

Alter table old_table_name rename [to] new_table_name

To can be omitted from writing

Example: change the table name t_dept to tab_dept

Alter table t_dept rename to tab_dept

Change table tab_dept to dept

Alter table tab_dept rename dept

② adds fields to the table

By default, add a field to the last column of the table

Syntax: alter table table_name add column name data type

Example: add a column to the dept table, column name descri, description, string type

Alter table dept add descri char (10)

Add a field to the first column of the table

Syntax: alter table table_name add column name data type first

Example: add id to the first column of the dept table, which is an integer type

Alter table dept add id int first

Add a new field after the specified field in the table

Syntax: alter table table_name add new column name data type after specifies the column name

Example: add the age column after the deptno column in the dept table to indicate the age, which is an integer type

Alter table dept add age int (3) after deptno

③ delete field

Syntax: alter table table_name drop column name

Example: delete the age column from the dept table

Alter table dept drop age

④ modify field

1. Modify the data type of the field

Syntax: alter table table_name modify column name data type

[description: the column name is the column to be modified, and the data type is the modified data type]

Example: change the data type of the loc column in the dept table to varchar (50).

Alter table dept modify loc varchar (50)

2. Modify the name of the field

Syntax: alter table table_name change old column name new column name old column data type

Example: change the descri column name in the dept table to the description column name.

Alter table dept change descri description char (10)

3. Modify the field name and data type at the same time

Syntax: alter table table_name change old column name new column name new column data type

Example: change the id name in the dept table to num and the data type from int to double.

Alter table dept change id num double

⑤ modifies the order of fields

Syntax 1:alter table table_name modify column name data type first

[description: adjust a column to the first column]

Example: adjust the loc column in the dept table to the first column

Alter table dept modify loc varchar (50) first

Syntax 2:alter table table_name modify column 1 column 1 data type after column 2

[description: after adjusting column 1 to column 2]

Example: after adjusting the num column in the dept table to dname

This is the end of alter table dept modify num double after dname; 's introduction to "what are the basic operations of MySQL". Thank you for reading. If you want to know more about the industry, you can follow the industry information channel. The editor will update different knowledge points for you every day.

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