Enforcing business rules using CHECK constraints

SQL Server allows you define column level CHECK constraints which check the integrity of a single column. Furthermore, SQL Server allows you to check the values of multiple columns together using a "table level" CHECK constraint. Though they're labeled as "table level" constraints, these type of CHECK constraints are actually checked at the row level. Lastly, CHECK constraints work by examining a defined condition to see if it evaluates to either TRUE or FALSE.

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