Updating joined tables
You can think of update queries as a powerful form of the Find and Replace dialog box.You cannot use an update query to add new records to a database, or to delete records from a database.When a view is created, Oracle Database expands any wildcard (*) in a top-level view query into a column list.The resulting query is stored in the data dictionary; any subqueries are left intact.When you need to update data from one table to another, consider the following rule: the data types for the source and destination fields must either match or be compatible.Furthermore, when you update data from one table to another and use compatible data types instead of matching data types, Access converts the data types of those fields in the destination table.
So, a key-preserved table has its keys preserved through a join.To add new records to a database you use an append query, and to delete whole records from a database you use a delete query.Here are the similarities and differences between Find and Replace and an update query: Like the Find and Replace dialog box, an update query lets you specify which value is being replaced, and what the new value is.You can use views in almost the same way as tables.
You can query, update, insert into, and delete from views, just as you can standard tables.
SELECT * FROM Division1_staff; ENAME EMPNO JOB DNAME ------------------------------------------------------ CLARK 7782 MANAGER ACCOUNTING KING 7839 PRESIDENT ACCOUNTING MILLER 7934 CLERK ACCOUNTING ALLEN 7499 SALESMAN SALES WARD 7521 SALESMAN SALES JAMES 7900 CLERK SALES TURNER 7844 SALESMAN SALES MARTIN 7654 SALESMAN SALES BLAKE 7698 MANAGER SALES This error message is returned when a view exists but is unusable due to errors in its query (whether it had errors when originally created or it was created successfully but became unusable later because underlying objects were altered or dropped). Additionally, if a view is a join on other nested views, then the other nested views must be mergeable into the top level view.