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Input Parameters datetime expression datetime expression datetime expression
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Function TIME WEEK YEAR
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Purpose Returns the time part of a date or datetime expression Returns the week of the year as an integer in the range 1 to 54 Returns the year part of a date or datetime expression
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From 1, you should recall that a view is a stored database query that provides a database user with a customized subset of the data from one or more tables in the database. Note that Microsoft Access uses the term query instead of view. The inherent beauty of views is that, once created, they can be queried just like tables. In fact, the user never needs to know they are using a view instead of a real table. There can be some restrictions when data manipulation (inserts, updates, and deletes) is attempted using views (check your DBMS documentation), but queries work just the same against views as they do against tables. Furthermore, views provide a number of very useful bene ts: Hiding columns a user does not need or should not see Hiding rows a user does not need or should not see Hiding complex operations such as joins Improving query performance (in some RDBMSs, such as Microsoft SQL Server) The examples in this section show views that provide the aforementioned bene ts. From 4, the general syntax for creating a view is
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CREATE [OR REPLACE] VIEW view_name AS sql_query;
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Here are some practical examples using the video store sample database: Obvious privacy rules require that the store manager keep employee tax IDs (social security numbers) and rates of pay in strict con dence. However, there are a number of web-based applications that require some employee information, such as the name of the employee and their supervisor s name (if any). What is required in such cases is a view that can be safely used by those web applications without the possibility of a developer who s using the data accidentally revealing con dential information. The query in the view must join with the PERSON table to nd the name of the employee
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and again (using an outer join) for the name of the employee s supervisor. Furthermore, column names should be as user friendly to a U.S.-based web development team as possible. Here is the SQL statement to create the view:
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CREATE VIEW EMPLOYEE_LIST AS SELECT A.PERSON_ID AS ID, B.PERSON_GIVEN_NAME AS FIRST_NAME, B.PERSON_MIDDLE_NAME AS MIDDLE_NAME, B.PERSON_FAMILY_NAME AS LAST_NAME, C.PERSON_GIVEN_NAME AS MANAGER_FIRST_NAME, C.PERSON_FAMILY_NAME AS MANAGER_LAST_NAME FROM EMPLOYEE A JOIN PERSON B ON A.PERSON_ID = B.PERSON_ID LEFT OUTER JOIN PERSON C ON A.SUPERVISOR_PERSON_ID = C.PERSON_ID View created.
Once the view is created, you can write queries against it just like you can with tables. Here is a simple query against the view just created:
SELECT LAST_NAME, MANAGER_LAST_NAME FROM EMPLOYEE_LIST ORDER BY LAST_NAME; LAST_NAME ------------------------Alexander Bernstein Chung MANAGER_LAST_NAME ------------------------Alexander Alexander
For a movie catalog listing, you want to list the MPAA Rating Description and the Movie Genre Description. It seems obvious that this three-table join will be needed quite often, so you help the video store staff by creating a view with the joins already done for them. Here is the SQL statement to create the view:
CREATE VIEW MOVIE_LISTING AS SELECT A.MOVIE_ID, B.MOVIE_GENRE_DESCRIPTION AS GENRE, C.MPAA_RATING_CODE AS RATING, C.MPAA_RATING_DESCRIPTION AS RATING_DESC, A.MOVIE_TITLE, A.RETAIL_PRICE_VHS, A.RETAIL_PRICE_DVD, A.YEAR_PRODUCED FROM MOVIE A JOIN MOVIE_GENRE B ON A.MOVIE_GENRE_CODE = B.MOVIE_GENRE_CODE JOIN MPAA_RATING C ON A.MPAA_RATING_CODE = C.MPAA_RATING_CODE
Advance Query Writing
Here is a simple query that uses the view instead of the base tables:
SELECT GENRE, RATING, MOVIE_TITLE FROM MOVIE_LISTING ORDER BY GENRE, RATING, MOVIE_TITLE; GENRE -------------------Action and Adventure Action and Adventure Action and Adventure Action and Adventure Action and Adventure Action and Adventure Action and Adventure Comedy Comedy Comedy Comedy Drama Drama Drama Drama Drama Drama Foreign Romance Romance 20 rows selected. RATING -----PG-13 PG-13 PG-13 PG-13 R R R PG-13 PG-13 PG-13 PG-13 PG-13 R R R R R R PG-13 PG-13 MOVIE_TITLE -----------------------------Master and Commander: The Far Pirates of the Caribbean: The The Day After Tomorrow The Italian Job Kill Bill: Vol. 1 Man on Fire The Last Samurai 50 First Dates Matchstick Men Something s Gotta Give The School of Rock Big Fish Cold Mountain Lost in Translation Monster Mystic River Road to Perdition Das Boot 13 Going on 30 Two Weeks Notice
The video store is very interested in placing a computer-based kiosk in the children s section to allow youngsters to search for movies online. However, the store manager wants to be sure only G, PG, and PG-13 rated movies show up on the children s kiosk. It would be simple enough to enforce this rule in the application program that will control the kiosk. However, if a database view is used and the kiosk application is forced to use only the view, there can be no accidental slip-ups in the application program s logic, and it will be easy to adjust the view later if the MPAA changes its rating system again (as they have done several times in the past). Rather than repeat the join logic in the MOVIE_LISTING view again in this view, you can simply use the MOVIE_LISTING view to create the
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