What are the basic operations of MySQL?

1. Library operation

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

show databases;

Create a library create database database_name;

create database test11;

Database_name naming convention for the library name ：

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

(2) The first letter cannot be a number and $

(3) It cannot be Keywords of mysql database

(4) Spaces and special characters are not allowed

(5) The length is less than 128 bits

Use a library

use database_name;

Check which library is currently used/connected

elect database();

View all tables under the current library

 show tables;

Delete a library

drop database database_name;

2. Table operations

Table is a very important object in the MySQL database and is the basic element of the database. The table is composed of rows and columns and is mainly used to store data.

Example: Store data in the form of a table

Student number, name, age, grade

1 Zhang San 30 100

2 Li Si 25 90

Create table

Syntax:

create table table_name(
            列名1 数据类型,
            列名2 数据类型,
            列名3 数据类型,
            列名4 数据类型,
            ....
            列名n 数据类型
         );

create table mytest(
      id int,
      name varchar(20),
      age int,
      birthday date
   );
  select * from mytest;

Data type:

Integer int (number of digits)

Decimal type/floating point type double

String type varchar (number of digits) variable length

char (number of 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 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 table structure

desc table_name;

View table detailed definition

 show create table table_name;

desc t_dept;
show create table t_dept;
show create table t_dept\G;

   （\G代替;能够让显示结果更美观）

Delete table

Delete a table

drop table table_name;

drop table t_dept;`

Modify table

①Modify table name

Syntax:

alter table old_table_name rename [to] new_table_name;

to can be omitted or not written

Example: change the table name t_dept to tab_dept

alter table t_dept rename to tab_dept;

will Table tab_dept is modified to dept

alter table tab_dept rename dept;

②Add fields to the table

By default, fields are added 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. The column name is descri, indicating description. The string type

alter table dept add descri char(10);

is added to the first column of the table. Field

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 of the table

Syntax:alter table table_name add new column name data type after specified column name;

Example: in dept Add the age column after the deptno column in the table, indicating age, which is an integer type

alter table dept add age int(3) after deptno;

③Delete field

Syntax: alter table table_name drop column name;

Example: Delete the age column in the dept table

alter table dept drop age;

④Modify the field

1. Modify the data type of the field

Syntax: alter table table_name modify column name data type;

[Explanation: 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 name and data type of the field 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 change the data type from int to double.

 alter table dept change id num double;

⑤Modify 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: Adjust column 1 to after column 2]

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

alter table dept modify num double after dname;

The above is the detailed content of What are the basic operations of MySQL?. For more information, please follow other related articles on the PHP Chinese website!