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
