Oracle Check Constraint tips

Oracle Check Constraint

Oracle check constraint insures that updated or inserted values meet a specific condition.  The Oracle check constraint check condition must return a TRUE or FALSE, much Like the WHERE clause.  If the Oracle check constraint condition returns as TRUE when you use Oracle check constraint, the value is accepted by the constraint. If Oracle check constraint returns the condition as FALSE, the value is rejected. Below, we include an Oracle check constraint on the editor_active column of the EDITOR table that insures the value is either Y or N.

To put it another way, Oracle check constraint validates incoming columns at row insert time. With Oracle check constraint, rather than having an application verify that all occurrences of REGION are North, South, East, or West, an Oracle CHECK constraint can be added to the table definition to ensure the validity of the region column.

Here is an example of Oracle check constraint:

Oracle check constraint has some limitations.  For one, subqueries cannot be used within your Oracle check constraints.  Also, an Oracle check constraint is able to reference another column. Sysdate, currval, nextval, level, rowid, uid, user or userenv cannot be referenced with Oracle check constraint.

Oracle check constraint cannot reference columns from other tables. There can be more than one Oracle check constraint per column, however the values being checked with Oracle check constraint must pass all Oracle check constraints on that column before being acceptable.  Oracle check constraint can also be used to check multiple columns. 

Oracle check constraint does have some limitations in its ability to validate data.  If more than one capable Oracle check constraint is needed, triggers must be implemented.