A check constraint is a rule that specifies the values that are allowed in one or more columns of every row of a base table.

Like referential constraints, check constraints are optional and you define them by using the CREATE TABLE and ALTER TABLE statements. The definition of a check constraint restricts the values that a specific column of a base table can contain.

A table can have any number of check constraints. DB2® enforces a check constraint by applying the restriction to each row that is inserted, loaded, or updated. One restriction is that a column name in a check constraint on a table must identify a column of that table.

CHECK (SALARY>= 30000)