Oracle views encapsulate a complex query and should be used with the utmost care. Hints can be used for specific SQL optimization, but use with views isn’t recommended. When the optimizer becomes “confused,” it will perform a full-table scan. Hints and views: Views aren’t finite tables, and adding SQL hints to view queries often results in poorly performing execution plans.Querying subsets: Developers often query a subset of a complex view, without realizing all the tables within the view will be joined.This will result in execution plans being suboptimal. Adding complicated WHERE clauses: When a query is performed against a view with complex WHERE clauses, it can override tuning hints within the view.If you choose to work with complex views, here are some circumstances you should avoid, unless it’s not possible to do so: The use of complex views to represent a large subset of your scheme, and to allow end users and developers to access these views, is likely to result in poor performance. WHERE emp.deptno = ptno Potential Issues With Views SELECT emp.empno, emp.ename, emp.job, emp.deptno, dept.dname, dept.loc This informs Oracle of how the modifications relate to the base table or tables.Ī complex view might look something like this: If you want to enable DML operations on complex views, you’ll need to include INSTEAD OF triggers in your query. DML operations cannot be performed directly against complex views. Complex views can contain a group by clause, an order by clause, and join conditions.

A simple view might look something like this:Ī complex view, unlike a simple view, can be constructed on more than one base table. DML changes are then applied to the base table of the view. Data Manipulation Language (DML) operations can be performed directly against simple views. Simple ViewsĪ simple view can only contain a single base table. Oracle views can be classified as either complex or simple. View details can be queried from within the data dictionary, by using ALL_VIEWS, USER_VIEWS, or DBA_VIEWS. The benefits of using views include reducing the complexity of SQL statements, hiding the NAME and OWNER of the base table, and only sharing specific table rows with other users. Views are useful for several purposes, including information hiding and security, but they can be problematic if they’re nested too deeply. It can be helpful to think of a view as a virtual table, or as the process of mapping data from one or more tables. Views are simply stored queries that can be executed when needed, but they don’t store data. This article will outline the basics of Oracle view performance tuning and explain how SolarWinds ® Database Performance Analyzer (DPA) can be used to speed up Oracle view performance.Īn Oracle view is a validated and named SQL query stored in the Oracle Database’s data dictionary. Understanding the difference between a standard SQL query and an Oracle view is an important aspect of performance tuning.

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