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)
>          ) ;

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