Meet SQL (2)


SQL self study notes


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