It s Your Turn to Create a Constraint in Font

Printer PDF 417 in Font It s Your Turn to Create a Constraint

It s Your Turn to Create a Constraint
Create PDF 417 In None
Using Barcode generator for Font Control to generate, create PDF 417 image in Font applications.
www.OnBarcode.com
Code 128 Generation In None
Using Barcode generator for Font Control to generate, create Code 128A image in Font applications.
www.OnBarcode.com
Too much talking and not enough walking! Guess what It s time to put you to work on creating a primary key constraint against the publication table. 1. Write a DDL script to create a primary key constraint against the publication table. (Hint: there are two columns in this primary key: id and title.) 2. Save the DDL script with the same filename as your constraint name, but with a .pkc extension. 3. Execute your script in SQL*Plus by typing an at sign (@) followed by the filename at the SQL> prompt.
Barcode Printer In None
Using Barcode generator for Font Control to generate, create Barcode image in Font applications.
www.OnBarcode.com
Encode EAN-13 Supplement 5 In None
Using Barcode maker for Font Control to generate, create EAN-13 image in Font applications.
www.OnBarcode.com
CHAPTER 1 GEN ESIS
Barcode Creation In None
Using Barcode generator for Font Control to generate, create Barcode image in Font applications.
www.OnBarcode.com
Code-39 Creation In None
Using Barcode generator for Font Control to generate, create ANSI/AIM Code 39 image in Font applications.
www.OnBarcode.com
The primary key constraint should now exist against the publication table in the database, just waiting for you to slip up and try putting in a duplicate row (or as Clint Eastwood would say, Go ahead punk, make my day. ). Otherwise, try to make some sense out of the error message(s) you got, correct your script, and then try again. My version of a DDL script to create a primary key constraint against the publication table is shown in Listing 1-9. Listing 1-9. DDL for Creating a Primary Key Constraint Against the Publication Table, publication_pk.pkc 1 2 3 4 5 ALTER TABLE publication ADD CONSTRAINT publication_pk PRIMARY KEY ( id, title);
PDF 417 Generation In None
Using Barcode creation for Font Control to generate, create PDF 417 image in Font applications.
www.OnBarcode.com
Uniform Symbology Specification Code 93 Creation In None
Using Barcode creation for Font Control to generate, create Uniform Symbology Specification Code 93 image in Font applications.
www.OnBarcode.com
Now you know how to create a table along with any required indexes and constraints, what do you do if you need a really complex constraint Or, how about if you need other actions to be triggered when a row or column in a table is inserted, updated, or deleted Well, that s the purpose of triggers.
Encode PDF 417 In None
Using Barcode drawer for Excel Control to generate, create PDF 417 image in Office Excel applications.
www.OnBarcode.com
PDF 417 Generator In C#.NET
Using Barcode generation for .NET Control to generate, create PDF-417 2d barcode image in VS .NET applications.
www.OnBarcode.com
Triggers
Drawing QR Code In Objective-C
Using Barcode creator for iPhone Control to generate, create Denso QR Bar Code image in iPhone applications.
www.OnBarcode.com
QR Code JIS X 0510 Recognizer In .NET
Using Barcode decoder for .NET Control to read, scan read, scan image in VS .NET applications.
www.OnBarcode.com
Triggers are PL/SQL programs that are set up to execute in response to a particular event on a table in the database. The events in question can take place FOR EACH ROW or for a SQL statement, so I call them row-level or statement-level triggers. The actual events associated with triggers can take place BEFORE, AFTER, or INSTEAD OF an INSERT, an UPDATE, or a DELETE SQL statement. Accordingly, you can create triggers for any of the events in Table 1-4.
Printing GS1-128 In Objective-C
Using Barcode printer for iPhone Control to generate, create EAN128 image in iPhone applications.
www.OnBarcode.com
Encoding Barcode In None
Using Barcode generator for Word Control to generate, create Barcode image in Microsoft Word applications.
www.OnBarcode.com
Table 1-4. Possible Trigger Events Against a Table
Paint Code 39 In None
Using Barcode maker for Software Control to generate, create Code 3/9 image in Software applications.
www.OnBarcode.com
Drawing QR Code In None
Using Barcode maker for Online Control to generate, create Denso QR Bar Code image in Online applications.
www.OnBarcode.com
Event
Scanning UPC Symbol In None
Using Barcode decoder for Software Control to read, scan read, scan image in Software applications.
www.OnBarcode.com
Print UPC - 13 In None
Using Barcode maker for Software Control to generate, create EAN-13 Supplement 5 image in Software applications.
www.OnBarcode.com
BEFORE BEFORE BEFORE BEFORE BEFORE BEFORE AFTER AFTER AFTER AFTER
Code 128 Generator In Java
Using Barcode maker for Java Control to generate, create Code128 image in Java applications.
www.OnBarcode.com
Print Barcode In .NET Framework
Using Barcode drawer for ASP.NET Control to generate, create Barcode image in ASP.NET applications.
www.OnBarcode.com
DELETE DELETE INSERT INSERT UPDATE UPDATE DELETE DELETE INSERT INSERT
Level
FOR EACH ROW
FOR EACH ROW
FOR EACH ROW
FOR EACH ROW
FOR EACH ROW
C HA PTER 1 G ENES IS
Table 1-4. Possible Trigger Events Against a Table
Event
AFTER AFTER INSTEAD OF INSTEAD OF INSTEAD OF INSTEAD OF INSTEAD OF INSTEAD OF
UPDATE UPDATE DELETE DELETE INSERT INSERT UPDATE UPDATE
Level
FOR EACH ROW
FOR EACH ROW
FOR EACH ROW
FOR EACH ROW
So let s say we want to play a practical joke. Are you with me here We don t want anyone to ever be able to add the name Jonathan Gennick (my editor, who is actually a genius in his own right, but it s fun to mess with him) to our list of database geniuses. Listing 1-10 shows a trigger created to prevent such an erroneous thing from happening. Listing 1-10. A Trigger Against the Author Table, author_bir.trg 01 02 03 04 05 06 07 08 09 10 CREATE OR REPLACE TRIGGER author_bir BEFORE INSERT ON author FOR EACH ROW BEGIN if upper(:new.name) = 'JONATHAN GENNICK' then raise_application_error(20000, 'Sorry, that genius is not allowed.'); end if; END; / The syntax used in Listing 1-10 is as follows: CREATE [OR REPLACE] TRIGGER <trigger_name> BEFORE INSERT ON <table_name> FOR EACH ROW BEGIN <pl/sql> END; where <trigger_name> is the name of the trigger, <table_name> is the name of the table for which you re creating the trigger, and <pl/sql> is the PL/SQL program you ve written to be executed BEFORE someone INSERTs EACH ROW. The brackets ([ ]) around the OR REPLACE keyword denote that it is optional. The OR REPLACE clause will allow you to re-create your trigger if it already exists.
CHAPTER 1 GEN ESIS
Views
A view represents the definition of a SQL query (SELECT statement) as though it were just another table in the database. Hence, you can INSERT into and UPDATE, DELETE, and SELECT from a view just as you can any table. (There are some restrictions on updating a view, but they can be resolved by the use of INSTEAD OF triggers.) Here are just a few of the uses of views: Transform the data from multiple tables into what appears to be one table. Nest multiple outer joins against different tables, which is not possible in a single SELECT statement. Implement a seamless layer of user-defined security against tables and columns. Let s say we want to create a view that combines the author and publication tables so it s easier for a novice SQL*Plus user to write a report about the publications written by each author. Listing 1-11 shows the DDL to create a view that contains the required SQL SELECT statement. Listing 1-11. DDL to Create an Author_Publication View, author_publication.vw 1 2 3 4 5 6 7 8 CREATE OR REPLACE VIEW author_publication as SELECT author.id, author.name, publication.title, publication.written_date FROM author, publication WHERE author.id = publication.id; The syntax for the CREATE VIEW statement used in Listing 1-11 is as follows: CREATE [OR REPLACE] VIEW <view_name> AS <sql_select_statement>; where <view_name> is the name of the view (the name that will be used in other SQL statements as though it s a table name), and <sql_select_statement> is a SQL SELECT statement against one or more tables in the database. Once again, the brackets around the OR REPLACE clause denote that it is optional. Using OR REPLACE also preserves any privileges (grants) that exist on a view. That does it for our DML review. Now let s move on to the SQL for manipulating data SQL keywords like INSERT, UPDATE, DELETE, and SELECT.
Copyright © OnBarcode.com . All rights reserved.