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What is updatable view 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.
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.
How do I create an updatable view?
However, to create an updatable view, the SELECT statement that defines the view must not contain any of the following elements:
- Aggregate functions such as MIN, MAX, SUM, AVG, and COUNT.
- DISTINCT.
- GROUP BY clause.
- HAVING clause.
- UNION or UNION ALL clause.
- Left join or outer join.
Is it possible to update view in Oracle?
Answer: A VIEW in Oracle is created by joining one or more tables. When you update record(s) in a VIEW, it updates the records in the underlying tables that make up the View. So, yes, you can update the data in an Oracle VIEW providing you have the proper privileges to the underlying Oracle tables.
What is purpose of view creation?
Views can be used to aggregate rows (using GROUP BY and HAVING) of a table with better detail. The view is used to summarize the data from multiple tables so that views can be used to generate reports.
Can we use DML in view?
Yes, View Is Virtual table. In simple view We create view on single base table That’s why we can perform all DML operations.it also called as Updatable view. But In case of Complex view We create view on multiple base tables that’s why we cannot perform DML operations It is ReadOnly View (Only Select Operation).
How are the keys of a table preserved?
A table is key-preserved if every key of the table can also be a key of the result of the join. So, a key-preserved table has its keys preserved through a join.
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.
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.
When do you put a key on a table?
So, if you can assert that a given row in a table will appear at most once in the view — that table is “key preserved” in the view. It sounds backwards because in our example above — its T2 that needs a unique constraint on Y if we want T1 to be key preserved (you put the key on T2, not on T1 to key preserve T1!)