What is a view ?
If we have several tables in a db and we want to view only specific columns from specific tables we can go for views. It would also suffice the needs of security some times allowing specfic users to see only specific columns based on the permission that we can configure on the view. Views also reduce the effort that is required for writing queries to access specific columns every time.
Views cannot contain:
FOR UPDATE OF
UNION / UNION ALL
ORDER BY
FOR FETCH ONLY
OPTIMIZE FOR . . .
Certain Views Can Not Be Updated (I/U/D):
Joins
Column Functions
DISTINCT
GROUP BY / HAVING
Subquery w/ Same Inner & Outer Table
View Based on Read Only View
Certain Views Can Not Be Inserted To:
Derived Data *
Constants
Views Defined Without All
Columns Not Having a Default