Release 10.1A: OpenEdge Data Management:
SQL Development

Need for integrity constraints

Integrity constraints are necessary because data in a database must be valid and consistent at all times. Data might be inconsistent because of entry errors, duplicate entries of rows, or other violations.

For example, to properly track a company’s employee information, each employee should be assigned a unique identification number. To ensure this, specify a UNIQUE constraint on the column that contains the employee number (emp_no), as shown in Example 5–10.

Example 5–10: UNIQUE constraint

CREATE TABLE employee_info ( emp_no INTEGER NOT NULL UNIQUE, first_name VARCHAR(20) NOT NULL, last_name VARCHAR(20) NOT NULL, title VARCHAR(20) ) ;