MySQL To strengthen
Zerofill primary key auto_increment
primary key auto_increment
constraint Main table _ Side table _pk foreign key (id) reference Main table （id）;
constraint Main table _ Side table _pk foreign key (id) reference Main table （id）on update cascade on delete cascade Cascade modification cascading deletion
First normal form Each field is indivisible
Second normal form Each field has a dependency on the primary key
Third normal form In addition to the primary key, they are directly dependent on the primary key
Internal connection ：
Select * from a,b where a.id = b.id
Select * from a where inner join b on a.id = b.id
The left outer join 、 Right connection
Select * from a left outer join b on a.id = b.id
-- Use the left table as the main table To display Can show null
Call Stored procedure name – call
See all global variables show variables
Look at a global variable show @@ Variable name
Modify global variables set Variable name = value
Session variables set @ Variable name = value
View session variables select @ Variable name
Create trigger tri_ name after update on Table name for each row
Insert into Record sheet values(‘ Content ’);
-- Change Password
Update user set password = password(‘ New password ’) where user=’ user ’
-- Assign permissions
Grant select on database . Table name to ‘ user ’@‘localhost’identified by ‘ password ’;
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