Introduction to Oracle9i: SQL1 Views

Introduction to Oracle9i: SQL2 Chapter Objectives Create a view, using CREATE VIEW command or the CREATE OR REPLACE VIEW command Employ the FORCE and NO FORCE options State the purpose of the WITH CHECK OPTION constraint

Introduction to Oracle9i: SQL3 Chapter Objectives Explain the effect of the WITH READ ONLY option Update a record in a simple view Re-create a view Explain the implication of an expression in a view for DML operations Update a record in a complex view

Introduction to Oracle9i: SQL4 Chapter Objectives Identify problems associated with adding records to a complex view Identify the key-preserved table underlying a complex view Drop a view Explain inline views and the use of ROWNUM to perform a “TOP-N” analysis

Introduction to Oracle9i: SQL5 Views Permanent objects that store no data Display data contained in other tables Two purposes: –Reduce complex query requirements for novice users –Restrict users’ access to sensitive data

Introduction to Oracle9i: SQL6 Types of Views

Introduction to Oracle9i: SQL7 CREATE VIEW Command Use OR REPLACE if view already exists Use FORCE if underlying table does not exist at time of creation Provide new column names if necessary

Introduction to Oracle9i: SQL8 CREATE VIEW Options WITH CHECK OPTION constraint – if used, prevents data changes that will make the data subsequently inaccessible to the view WITH READ ONLY – prevents DML operations

Introduction to Oracle9i: SQL9 Simple View Only references one table – no group functions, GROUP BY clause, or expressions

Introduction to Oracle9i: SQL10 Simple View – DML Operations Any DML operations are allowed through simple views unless created with WITH READ ONLY option DML operations that violate constraints on the underlying table are not allowed

Introduction to Oracle9i: SQL11 Complex View May contain data from multiple tables or data created with the GROUP BY clause, functions, or expressions Type of DML operations allowed depends on various factors

Introduction to Oracle9i: SQL12 DML Operations - Complex Views with Expressions Values cannot be inserted into columns that are based on arithmetic expressions

Introduction to Oracle9i: SQL13 DML Operations – Complex Views from Multiple Tables DML operations can not be performed on non key-preserved tables, but they are permitted on key-preserved tables

Introduction to Oracle9i: SQL14 DML Operations – Other Complex Views No DML operations are permitted on complex views based on DISTINCT, ROWNUM, GROUP BY, or a function

Introduction to Oracle9i: SQL15 Dropping a View Use DROP VIEW command

Introduction to Oracle9i: SQL16 Inline View Temporary table created by using subquery in FROM clause Can only be referenced while the command is being executed Most common usage – “TOP-N” Analysis

Introduction to Oracle9i: SQL17 “TOP-N” Analysis ORDER BY included to identify top values: –descending for highest values, ascending for lowest values Extract data based on ROWNUM