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Restrictions on Check Constraints
* You cannot specify a check constraint for a view. However, you can define the view using the WITH CHECK OPTION clause, which is equivalent to specifying a check constraint for the view.
* The condition of a check constraint can refer to any column in the table, but it cannot refer to columns of other tables.
* Conditions of check constraints cannot contain the following constructs:
o Subqueries and scalar subquery expressions
o Calls to the functions that are not deterministic (CURRENT_DATE, CURRENT_TIMESTAMP, DBTIMEZONE, LOCALTIMESTAMP, SESSIONTIMEZONE, SYSDATE, SYSTIMESTAMP, UID, USER, and USERENV)
o Calls to user-defined functions
o Dereferencing of REF columns (for example, using the DEREF function)
o Nested table columns or attributes
o The pseudocolumns CURRVAL, NEXTVAL, LEVEL, or ROWNUM
o Date constants that are not fully specified
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