Meet SQL (2)

Time:2021-2-26

SQL self study notes

constraint

1.0 concept and classification

 

2.0 non NULL constraint

 

3.0 unique constraints

 

4.0 primary key constraints

 

Automatic growth

 

 

5.0 foreign key constraints

 

Cascade operation

 

 

Multi table relation

Overview of three situations

 

 

 

Backup and restore of database

 

 

multi-table query

1.0 inner connection query

Implicit join: eliminating useless data with where condition

Show internal connections:

2.0 external connection query

 

3.0 different sub queries