Database constraints and validity checks are sometimes loosely referred to as business rules (see“Semantic Data Integrity Constraints” on page 623, and “Semantic Constraint Specifications” on page 636). They define conditions that must be met before a given value is permitted to be written to a column such as value ranges, equality or inequality conditions, and intercolumn dependencies. Teradata Database supports constraints at both the column and table levels. Constraints are defined using the CREATE TABLE and ALTER TABLE SQL statements.
Note: You cannot define any type of database constraint on columns defined with a UDT, XML, BLOB, or CLOB data type.
Database triggers, too, are often referred to as business rules. They define certain actions that are to be taken when a particular condition occurs during the update of the table on which they are defined.
The Constraints form:
This form supports the second step in the ATM process (see “Goals” on page 123).