Chapter 4 of getting started with MySQL: creation, modification and deletion of data tables

1. Create database

Data table belongs to database , Before creating the database , You should use use < Database name > Specify the database in which the operation is performed .

1.1 Use create Statement create data table

Examples are as follows

First create and select the database

Log in and copy

create database company;
use company;
create table emp
(
id int,
name varchar(25),
sex tinyint,
salary float
);

     

      
1.
      
2.
      
3.
      
4.
      
5.
      
6.
      
7.
      
8.
      
9.
     

2. Look at the data table structure

2.1 View table basic structure

Use describe/desc Statement to view table field information .

Illustrate with examples

Enter the following code

Log in and copy

desc company;

     

      
1.
     

2.2 Look at the detailed structure of the table

Log in and copy

show create table emp;

     

      
1.
     

3. Modify data sheet

After the data table is created , You can also modify the data table according to the actual needs

3.1 Modify data table name

Table names are uniquely defined in a database , The database system distinguishes different tables by table names

Data table update code format

Log in and copy

alter table < The old name of the table > rename to < The new name of the table >

     

      
1.
     

for example

take company In the database emp Change the table to emps

Input sql sentence

Log in and copy

show tables;
alter table emp rename to emps;
show tables;

     

      
1.
      
2.
      
3.
     

3.2 Modify field data type

Change the data type of the field , Is to convert the data type of a field into another data type . stay MySQL The syntax format of modifying the field data type in is as follows :

Log in and copy

ALTER TABLE< Table name >MODIFY< Field name >< data type >;

     

      
1.
     

The main parameters are introduced as follows .
Table name : Refers to the name of the table where the field of the data type to be modified is located .

Field name : Refers to the field to be modified .

data type : Refers to the new data type of the modified field .

give an example

Check the data table before operation name type

Log in and copy

desc emps;

     

      
1.
     

modify name

Log in and copy

alter table emps modify name varchar(20);

     

      
1.
     

3.4 Modify the field name of the data table

After the field names in the data table are set , It's not static , You can modify the field name as needed .MySQL The syntax format of modifying the table field name in is as follows :

Log in and copy

ALTER TABLE< Table name >CHANGE< Old field name >< new field name >< New data types >;

     

      
1.
     

The main parameters are introduced as follows .

Table name : The data table of the field name to be modified . Old field name : Refers to the field name before modification .
new field name : Refers to the modified field name .

New data types : Refers to the modified data type , If you don't need to modify the data type of the field , You can set the new data type to be the same as the original , But the data type cannot be empty .

give an example