SQL ViewsChapter 3A

Appendix Objectives

• Learn basic SQL statements for creating views

• Learn basic SQL statements for using views

• Understand the reasons for using views

SQL Views

• A SQL view is a virtual table that is constructed from other tables or views

• A view has no data of its own, but uses data stored in tables or other views

• Views are created using SQL SELECT statements

• Views are used in other SELECT statements just as if they were a table

• The SQL statements that create the views may not contain an ORDER BY clause. If the results of a query using a view need to be sorted, the sort order must be provided by the SELECT statement that processes the view

• However, Oracle allows you to create the views that contain an ORDER BY clause

SQL CREATE VIEW Statement

• The SQL CREATE VIEW statement is used to create view structures.

CREATE VIEW ViewName AS

{SQL SELECT statement};

SQL CREATE VIEW Example

Create a view to list the city and product name for each product ordered by its quantity:

create view v_products as

select city, pname as myname from products order by quantity;

Using an SQL SELECT Statement

• Once the view is created, it can be used in the FROM clause of SELECT statements just like a table.

select * from v_products;

Some Uses for SQL Views

• Hide columns or rows• Display results of computations• Hide complicated SQL syntax• Layer built-in functions

Using SQL Views: Hide columns or rows I

Why do we want to hide columns/rows?1. simplify results2. security reasons

prevent the display of sensitive data

CREATE VIEW BasicDepartmentDataView AS SELECT DepartmentName,

Phone AS DepartmentPhone FROM DEPARTMENT;

SELECT * FROM BasicDepartmentDataViewORDER BY DepartmentName;

Using SQL Views: Hide columns or rows II

How do we hide rows?•Using WHERE clause

CREATE VIEW MarkingDepartmentProjectView AS SELECT ProjectID, Name AS ProjectName,

MaxHours, StartDate, EndDate FROM PROJECT WHERE Department = 'Marketing';

SELECT * FROM MarkingDepartmentProjectViewORDER BY ProjectID;

Using SQL Views: Display results of computations – SQL Statement

CREATE VIEW ProjectHoursToDateView ASSELECT PROJECT.ProjectID,

Name AS ProjectName,MaxHours AS ProjectMaxHours,SUM(HoursWorked) AS ProjectHoursWorkedToDate

FROM PROJECT, ASSIGNMENTWHERE PROJECT.ProjectID =

ASSIGNMENT.ProjectIDGROUP BY PROJECT.ProjectID;

Using SQL Views: Display results of computations – Results

SELECT * FROM ProjectHoursToDateViewORDER BY PROJECT.ProjectID;

Using SQL Views: Hide complicated SQL syntax – SQL Statement

CREATE VIEW EmployeeProjectHoursWorkedView ASSELECT Name, FirstName, LastName,

HoursWorkedFROM EMPLOYEE AS E JOIN ASSIGNMENT AS A

ON E.EmployeeNumber =A.EmployeeNumber

JOIN PROJECT AS PON A.ProjectID =

P.ProjectID;

Using SQL Views: Hide complicated SQL syntax – Results

SELECT * FROM EmployeeProjectHoursWorkedView;

Using SQL Views: Layering Computations and Built-in Functions

1st SQL Statement

CREATE VIEW ProjectHoursToDateView ASSELECT PPOJECT.ProjectID,

Name AS ProjectName,MaxHours AS ProjectMaxHours,SUM(HoursWorked) AS

ProjectHoursWorkedToDateFROM PROJECT, ASSIGNMENTWHERE PROJECT.ProjectID =

ASSIGNMENT.ProjectIDGROUP BY PROJECT.ProjectID;

Using SQL Views: Layering Computations and Built-in Functions

2nd SQL Statement

CREATE VIEW ProjectsOverAllotedMaxHoursView AS

SELECT ProjectID, ProjectName, ProjectMaxHours, ProjectHoursWorkedToDate

FROM ProjectHoursToDateView WHERE ProjectHoursWorkedToDate > ProjectMaxHours;

Using SQL Views: Layering Computations and Built-in Functions

Results

SELECT ProjectID, ProjectName, ProjectMaxHours, ProjectHoursWorkedToDate, (ProjectHoursWorkedToDate

- ProjectMaxHours) AS HoursOverMaxAllocated

FROM ProjectsOverAllotedMaxHoursViewORDER BY ProjectID;

SQL ViewsEnd of Presentation on Chapter 3A

DAVID M. KROENKE and DAVID J. AUER

DATABASE CONCEPTS, 5th Edition

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