The first chapter of the table constraint
1.1 concept
- Data in the table are defined to ensure the accuracy, effectiveness and integrity of data.
1.2 Classification
- Primary key constraints: primary key.
- Non-empty constraint: not null.
- The only constraint: unique.
- Foreign key constraint: foreign key.
Chapter II multi-table operations
Chapter Three Forms
Backup and Restore database Chapter IV
Chapter V multi-table query
Chapter VI subquery
Chapter VII Affairs
Chapter VIII of the user management and rights management