What do you mean by updatable view?

An updatable view is a special case of a deletable view. A column of a view is updatable when all of the following rules are true: The view is deletable. The column resolves to a column of a table (not using a dereference operation) and the READ ONLY option is not specified.

What are updatable views in Oracle?

An updatable view is one you can use to insert, update, or delete base table rows. You can create a view to be inherently updatable, or you can create an INSTEAD OF trigger on any view to make it updatable.

How do you make a updatable view?

However, to create an updatable view, the SELECT statement that defines the view must not contain any of the following elements:

1. Aggregate functions such as MIN, MAX, SUM, AVG, and COUNT.
2. DISTINCT.
3. GROUP BY clause.
4. HAVING clause.
5. UNION or UNION ALL clause.
6. Left join or outer join.

What are after triggers?

After triggers: used to access field values that are set by the system (such as a record’s Id or LastModifiedDate field) and to effect changes in other records. The records that fire the after the trigger is read-only. We cannot use After trigger if we want to update a record because it causes a read-only error.

Can a view be created without a table?

A view is simply a virtual table. Think of it as just a query that is stored on SQL Server and when used by a user, it will look and act just like a table but it’s not. It is a view and does not have a definition or structure of a table.

Can I insert into a view?

You can insert rows into a view only if the view is modifiable and contains no derived columns. When a modifiable view contains no derived columns, you can insert into it as if it were a table. The database server, however, uses NULL as the value for any column that is not exposed by the view.

What are the before triggers?

Before triggers are used to update or validate record values before they’re saved to the database. After triggers are used to access field values that are set by the system (such as a record’s Id or LastModifiedDate field), and to affect changes in other records. The records that fire the after trigger are read-only.

What is the purpose of instead of trigger?

An INSTEAD OF trigger is a trigger that allows you to update data in tables via their view which cannot be modified directly through DML statements. When you issue a DML statement such as INSERT , UPDATE , or DELETE to a non-updatable view, Oracle will issue an error.

What does it mean when a key is preserved in a table?

Key preserved means the row from the base table will appear AT MOST ONCE in the output view on that table.

When to extract columns from a key preserved table?

For an UPDATE statement, all columns updated must be extracted from a key-preserved table. If the view has the CHECK OPTION, join columns and columns taken from tables that are referenced more than once in the view must be shielded from UPDATE.

Do you need special treatment for key preserved tables?

If you want key preserved tables in a view, you must explicitly define the primary and foreign keys in the tables, or define unique indexes. The docs note that if you want a view to be inherently updatable, it must have special treatment for key preserved tables.

When to delete from a key preserved table in Oracle?

For an UPDATE statement, all columns in the SET clause must belong to a key-preserved table. For a DELETE statement, if the join results in more than one key-preserved table, the Oracle deletes from the first table in the FROM clause.