CS 3630 Database Design and Implementation

Base Table and View• Base Table Stored on disk • View Virtual table Records are not stored on disk Query is stored Records are generated when requested

Looks like a table The users don’t know the difference

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Horizontal views (a subset)

Create View HotelsOfGlasgow asSelect *From HotelWhere Name = 'Glasgow';

Desc HotelsOfGlasgow

select * from HotelsOfGlasgow;

Drop View RoomsInHotel;

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Vertical View (Projection)Table SchemaBooking (Hotel_no, Guest_no, Date_from, Date_to, Room_No)

Create or replace view HotelBooking as Select Hotel_no, Room_No, Date_from, Date_toFrom Booking;

-- Cannot use Create or replace for tables

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Horizontal and Vertical View

Create or replace view BookingOfGlasgow asSelect Room_No, Date_from, Date_toFrom BookingWhere Hotel_No in ('H05', 'H28');

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Horizontal and Vertical View

-- using view HotelsOfGlasgow Create or replace view BookingOfGlasgow as Select Room_No, Date_from, Date_toFrom BookingWhere Hotel_No in (Select Hotel_No From HotelsOfGlasgow);

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Views based on grouping

-- must give names to aggregate functions -- and all fields when one aggregate -- function exists. Create or replace view RoomsInHotel (Hotel_no, Room_Count) as Select Hotel_no, Count(*) From Room Group By Hotel_No;

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Using Views in Queries

Create or Replace View HotelG As Select Hotel_No From Hotel Where Name = 'Grosvenor';

Select * From Room Where Hotel_No in HotelG;

ERROR at line 3:ORA-00904: "HOTELG": invalid identifier

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Using Views in Queries

Create or Replace View HotelG As Select Hotel_No From Hotel Where Name = 'Grosvenor';

Select * From Room Where Hotel_No in (Select * from HotelG);

-- works if one value from the view Where Hotel_No = (Select * from HotelG);

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Sub-Queries

-- List guests who don’t have any bookings during-- April 2005.

Select *From guestWhere guest_no Not IN (Select Distinct guest_no From booking Where date_from <= '30-Apr-05' and date_to >= '01-Apr-05');

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Using View-- List guests who don’t have any bookings for -- April 2005.

Create or Replace View BookingApril2005 as(Select guest_no From booking

Where date_from <= '30-Apr-05' and date_to >= '01-Apr-05');

Select *From guestWhere guest_no Not IN BookingApril2005;

ORA-00904: "BOOKINGAPRIL2005": invalid identifier

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Using View-- List guests who don’t have any bookings for -- April 2005.

Create or Replace View BookingApril2005 as(Select guest_no From booking

Where date_from <= '30-Apr-05' and date_to >= '01-Apr-05');

Select *From guestWhere guest_no Not IN (Select * From BookingApril2005);

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Using WITH

With BookingApril2005 as(Select guest_no From booking

Where date_from <= '30-Apr-05' and date_to >= '01-Apr-05')Select *From guestWhere guest_no Not IN (Select * From BookingApril2005);

Must have () for the With sub-query

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Outer Join

-- List guests who don’t have any bookings during-- April 2005.

Select G.*From guest GLeft Join Booking B on G.guest_no = B.guest_no and date_from <= '30-Apr-05' and date_to >= '01-Apr-05'Where B.guest_no is null;

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Database System and File System

Views in a File System?

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Database Views

• Look like base tables• Used in queries the same way as base tables• Insert?• Delete?• Update?

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Insert/Delete/Update Views

-- View based on groupCreate or Replace view RoomsInHotel(Hotel, Room_Count) as Select Hotel_no, Count(*) From Room Group By Hotel_No;

Insert into RoomsInHotel Values ('H11', 5); -- should insert 5 records into Room with 'H11' -- which 5 rooms? -- RNo (part of PK) not specified.-- Cannot do it!

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Assignmet 9

Any Questions?

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Phase III

Any Questions?

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Schedule• Assignment 10

Start Friday

• Quiz 4Friday May 1

• Test 2Wednesday, May 6

• Phase IVFriday, May 8

• Final ExamThursday, May 147 PM (Group #10)

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