Start Updating schema

Updating schema

For information changing conditions and their impact on views, see 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.

If developers have such constructs in applications, then you should encourage the developers to replace them with access to sequences.

Sequences eliminate serialization and improve the concurrency of an application.

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.

SELECT COLUMN_NAME, UPDATABLE FROM USER_UPDATABLE_COLUMNS WHERE TABLE_NAME = 'EMP_DEPT'; COLUMN_NAME UPD ------------------------------ --- EMPNO YES ENAME YES DEPTNO YES SAL YES DNAME NO LOC NO 6 rows selected.

statement lets you locate recompilation errors before run time.

A new primary key value can be obtained by selecting the most recently produced value and incrementing it.

This method requires a lock during the transaction and causes multiple users to wait for the next value of the primary key; this waiting is known as .

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.

Note: One special type of view is the editioning view, which is used only to support online upgrade of applications using edition-based redefinition.