- The RDBMS checks data (insert, update, delete) to avoid
- Several levels of data integrity:
- NOT NULL: complain if no value given.
- PRIMARY KEY: values must be unique in the table.
- FOREIGN KEY: the row referred to must exist.
- Transactions: a set of operations must all succeed, or all
changes in the set are rolled back (COMMIT, ROLLBACK). This is
extremely useful for complex databases.
- Data locking, to prevent others from accessing data being changed.
- All SQL-compliant systems should make these checks, but not all
have implemented this.
- Used in the right way, can stop mistaken operations from damaging
- If wrong design, then data integrity constraints may complicate
updates (circular foreign keys).
- These checks require computation: no free lunch!
© 2001 Per Kraulis
$Date: 2001/05/09 14:18:27 $