What are the limitations of CHECK constraint?

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The main limitation of CHECK constraint is that the condition must be a Boolean expression evaluated using the values in the row being inserted or updated and can’t contain sub queries.

In Oracle, CHECK constraints have certain limitations. Some of the notable limitations include:

  1. Complex Conditions: CHECK constraints can become complex and may be challenging to express certain complex conditions using them.
  2. No Subqueries: CHECK constraints cannot contain subqueries. You can only use scalar expressions, which means you cannot reference data from other tables in the CHECK constraint.
  3. No References to Other Tables: While you can reference columns within the same table, you cannot reference columns from other tables in a CHECK constraint.
  4. No Dynamic Conditions: CHECK constraints are evaluated at the time of the statement that triggers them. They cannot be used for dynamic conditions that change over time; they are static conditions based on the values in the row being modified.
  5. Null Values: CHECK constraints are not evaluated for NULL values. If you want to enforce conditions on columns with NULL values, you might need to use other mechanisms like triggers.
  6. No Complex Integrity Rules: While CHECK constraints are useful for simple integrity rules, more complex integrity rules or those involving multiple tables are better implemented using triggers or other mechanisms.

It’s important to carefully consider these limitations when designing your database schema and enforcing data integrity using CHECK constraints in Oracle. If your requirements go beyond what CHECK constraints can offer, you might need to explore other options like triggers, stored procedures, or application-level validation.