Chapter 7. Logical Consistency

A key strength of any modern relational database is its ability to validate the information stored in the database. One way the database itself can perform validation is by the use of constraints on a column or columns in a table. A constraint on a table column restricts the type of information in the column. A constraint can ensure that data is not omitted from a column, is within a certain range, is unique within the table, or exists in another table.

A second way to maintain the logical consistency in a database is the ability to "group" several SQL statements together in a transaction, where either all of these SQL statements succeed or all of them fail. This group of SQL statements is considered a logical unit of work. You can control transaction processing by using the COMMIT and ROLLBACK statements.