MySQL table operation

1. Create table

grammar :

CREATE TABLE table_name ( 
field1 datatype, 
field2 datatype, 
field3 datatype 
) character set  Character set  collate  Validation rules  engine  Storage engine ;

• fifield Said column names
• datatype Indicates the type of the column
• character set Character set , If no character set is specified , Then the character set of the database shall prevail
• collate Validation rules , If no verification rule is specified , The verification rules of the database shall prevail

        

                

2. Create a table case

create table users ( 
id int, 
name varchar(20) comment ' user name ', 
password char(32) comment ' password ', 
birthday date comment ' Birthday ' 
) character set utf8 engine MyISAM; 

① Different storage engines , The file that creates the table is different .

users The table storage engine is MyISAM , There are three different files in the data entry , Namely ：

• users.frm： Table structure
• users.MYD： Table data
• users.MYI： Table index

                 

②comment Followed by comments

                 

                        

3. View table structure

(1)desc The name of the table ;

(2) show create table The name of the table \G;

                

                

4. Modify table

(1) In the actual development of the project , Often modify the structure of a table , For example, field name , Field size , Field type , The character set type of the table , Table storage engine and so on . We still have needs , Add fields , Delete fields and so on . Then we need to modify the table .

ALTER TABLE tablename ADD (column datatype [DEFAULT expr][,column datatype]...); 
ALTER TABLE tablename MODIfy (column datatype [DEFAULT expr][,column datatype]...); 
ALTER TABLE tablename DROP (column);

                         

(2) When we create database tables , It is not recommended to modify the established table structure ; If the table is really created incorrectly, don't change it , Recreate ﹔ Don't change the table structure easily , Changes may cause serious errors , The table structure determines how the upper business is written .
                 

(3) Example

① stay users Add two records to the table

insert into users values(1,' Zhang San ','123456','2001-1-1'),(2,' Li Si ','88888','2002-1-1');

                 

② stay users Table add a field , Used to save the picture path

alter table users add path varchar(100) comment ' Picture path ' after id;

•  after Following the column name means that the new column is after the column , without after, The default is in the last column .
• After inserting the new field , It has no effect on the data in the original table

                 

③ modify name, Change its length to 60 

alter table users modify name varchar(60);

• modify It is an overlay modification  

                

④ Delete password Column

 alter table users drop password;

• Be careful when deleting fields , The deleted field and its corresponding column data are gone  

                 

⑤ Change the table name to person 

alter table users rename to person;

• to It can be omitted  

                 

 ⑥ Add column name id It is amended as follows flag

alter table person change id flag int comment ' Identify a user ';

•   The new field needs to be fully defined ( type ).

                

⑦ Summary

The table structure should not be deleted easily in the working scenario , Make a backup before deleting

alter table  Your watch name  add/modify/drop   Column + Column properties ;
alter table  Your watch name  rename  New table name ;
alter table  Your watch name  change  Old column name    New column + Properties of the new column ;

                                 

 4. Delete table

drop table student;