MySQL Common commands

The following articles mainly introduce common MySQL commands and the collation of common MySQL commands. We all know that the proportion of commonly used MySQL commands in actual applications is relatively large, today, we will give you a detailed description of common MySQL commands. MySQLuseimss; MySQLselectif (exists (select * frominf

The following articles mainly introduce common MySQL commands and the collation of common MySQL commands. We all know that the proportion of commonly used MySQL commands in actual applications is relatively large, today, we will give you a detailed description of common MySQL commands. MySQL useimss; MySQL selectif (exists (select * frominf

The following articles mainly introduce common MySQL commands and the collation of common MySQL commands. We all know that the proportion of commonly used MySQL commands in actual applications is relatively large, today, we will give you a detailed description of common MySQL commands.

Exist?

 
 

  
  
MySQL> use imss; 
  
  
MySQL> select if(exists(select * from information_schema.columns where table_name = 
'imss_righttemplate' and column_name='id_righttemplate'),'yes','no') as cz ; 
 
 

Common MySQL commands: Primary Key

 
 

  
  
MySQL> alter table tabelname add new_field_id int(5) unsigned default 0 not null auto_increment ,add primary key (new_field_id); 
 
 

Add a new column

 
 

  
  
MySQL> alter table t2 add d timestamp; 
  
  
MySQL> alter table infos add ex tinyint not null default '0'; 
 
 

Delete column

 
 

  
  
MySQL> alter table t2 drop column c; 
 
 

Rename a column

 
 

  
  
MySQL> alter table t1 change a b integer; 
 
 

Change column type

 
 

  
  
MySQL> alter table t1 change b b bigint not null; 
  
  
MySQL>alter table infos change list list tinyint not null default '0'; 
 
 

Common MySQL commands: rename a table

 
 

  
  
MySQL> alter table t1 rename t2; 
 
 

Add Index

 
 

  
  
MySQL> alter table tablename change depno int (5) not null;
  
  
MySQL> alter table tablename add index name (field name 1 [, field name 2…]);
  
  
MySQL> alter table tablename add index emp_name (name );
 
 

Index with primary keywords

 
 

  
  
MySQL> alter table tablename add primary key(id); 
 
 

Add an index with unique conditions

 
 

  
  
MySQL> alter table tablename add unique emp_name2(cardnumber); 
 
 

Delete An index

 
 

  
  
MySQL>alter table tablename drop index emp_name; 
 
 

Add Field

 
 

  
  
MySQL> ALTER TABLE table_name ADD field_name field_type; 
 
 

Modify the original field name and type

 
 

  
  
MySQL> ALTER TABLE table_name CHANGE old_field_name new_field_name field_type; 
 
 

Delete Field

 
 

  
  
MySQL> ALTER TABLE table_name DROP field_name; 
 
 

The above content is an introduction to common MySQL commands. I hope you will find some gains.