1. What is the purpose of field constraints ?
Database constraint is used to ensure that data means to meet the business rules, conditions do data limitations.
2. Type field there are several constraints ?
1. The primary key constraint ( a PRIMARY KEY )
2. The only constraint ( UNIQUE)
3. Non-empty constraint ( the NOT NULL)
4. Check constraints ( the CHECK)
The foreign key constraint ( a FOREIGN KEY)
3. The primary key constraint practice
4. The only constraint practice
5. Non-empty constraint practice
6. Check constraint practice
7. foreign key constraint practice
