The CHECK Constraint
You can use the CHECK constraint to enforce domain integrity and to provide a means for restricting the values that can be entered in a column. A CHECK constraint is implemented as a Boolean expression, and it must not be FALSE if the insertion or update is to proceed. The Boolean expression can reference other columns in the same table, but it cannot reference other tables. Foreign keys and triggers can be used to reference columns in other tables, if needed. The expression can also include functions that do not return results. A CHECK constraint that is defined on a specific column can reference only the values in the column.
CHECK constraints are good for ensuring the format of data inserted in a column and for defining ...
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