Simple Programming
Part 2
SECTION 8
CURSORS and TRIGGERS
Cursors
•An extremely important programming construct .
• Stands for:
– “Current set of records”
– It allows you to take a subset of data and output
the information in various ways.
CURSOR Commands:
1. The OPEN command
–
Opens the cursor for use
2. The FETCH command
–
Retrieves a specific row from a cursor
3. The CLOSE command
–
Closes an open cursor
4. The DEALLOCATE command
–
Removes the cursor
Cursor Declaration
• Declared in the following manner:
1.
2.
3.
4.
5.
6.
7.
Declare variables to hold the output from the cursor.
Declare the cursor object.
Assign the query to the cursor.
Open the cursor and fetch the first row
Loop until there are no more results. In the loop print out the Customer
Number and the Customer Last Name from the result set and fetch the net
Close the cursor.
Deallocate the cursor to free up any memory or open result sets.
The CUSTOMER Table
The following uses a CURSOR from the CUSTOMER table
1.
Declare variables to hold the output from the cursor.
DECLARE @CustomerNumber as numeric;
DECLARE @CustomerName as nvarchar(20);
2.
Declare the cursor object.
DECLARE @customer_cursor as CURSOR;
3.
Assign the query to the cursor.
SET @customer_cursor = CURSOR FOR
SELECT CustomerNUmber, CustomerName
FROM CUSTOMER;
4.
Open the cursor and fetch the fiurst row
OPEN @customer_cursor;
FETCH NEXT FROM @customer_cursor INTO @CustomerNumber, @CustomerName;
5.
Loop until there are no more results. In the loop print out the Customer Number and the Customer Last Name from the result set and fetch the
net row
WHILE @@FETCH_STATUS = 0
BEGIN
PRINT cast(@CustomerNumber as VARCHAR (50)) + ' ' + @CustomerName;
FETCH NEXT FROM @customer_cursor INTO @CustomerNumber, @CustomerName;
END
6.
Close the cursor.
CLOSE @customer_cursor;
7.
Deallocate the cursor to free up any memory or open result sets.
DEALLOCATE @customer_cursor;
What is in the cursor?
@CustomerNumber
@CustomerName
5155
George Black
5204
Stephanie Green
5255
Alice Van Dunn
5346
Bonnie Stewart
5389
Jake Solaris
5443
Jane Quicker
The following uses CONCAT using a CURSOR for CUSTOMER
DECLARE @Customer as nvarchar(30);
DECLARE @customer_cursor as CURSOR;
SET @customer_cursor = CURSOR FOR
SELECT CONCAT(CustomerNumber,’ - ‘, CustomerName)
FROM CUSTOMER;
OPEN @customer_cursor;
FETCH NEXT FROM @customer_cursor INTO @Customer
WHILE @@FETCH_STATUS = 0
BEGIN
PRINT @Customer
FETCH NEXT FROM @customer_cursor INTO @Customer
END
CLOSE @customer_cursor;
DEALLOCATE @customer_cursor;
Notice the dash mark ‘ - ‘
Notice the dash mark ‘ - ‘
The Chinese Zodiac Procedure using a cursor
The CHINESE_ZODIAC table will be the
basis of the cursor, zodiac_cursor
CREATE PROCEDURE Chinese_Zodiac_Proc05 (@birthyear NUMERIC)
--This procedure deals with birth years and the Chinese Zodiac
AS
DECLARE
@BD NUMERIC(5), @X NUMERIC(10,6), @Y NUMERIC(4), @Z NUMERIC(2),
@Number NUMERIC = 0,
@ZodiacSign nVARCHAR(10),
@zodiac_cursor as CURSOR
SET @zodiac_cursor = CURSOR FOR
select * from chinese_zodiac
BEGIN
SET @BD = @birthyear
--The following deals with BCE years. There is no year 0
IF @birthyear = 0
BEGIN
SET @birthyear = 1
PRINT 'Year 0 is not a vaild year. It should be year 1.'
END
IF @BD <1
SET @BD = @BD +1
SET @X = @BD/12
SET @Y = @BD/12
--The following reduces @Y by 1 when SQL Server rounds up a number to the next highest number.
IF @Y > @X SET @Y = @Y-1
SET @Z = (@X - @Y)*12
END
OPEN @zodiac_cursor
FETCH NEXT FROM @zodiac_cursor INTO @Number, @ZodiacSign
WHILE @@FETCH_STATUS = 0 and @Z <> @Number
FETCH NEXT FROM @zodiac_cursor INTO @Number,@ZodiacSign
PRINT CAST(@birthyear as nVARCHAR(20)) + ' ' + @ZodiacSign
PRINT '*****'
CLOSE @zodiac_cursor
DEALLOCATE @zodiac_cursor
WHERE CURRENT OF
• Syntax:
WHERE CURRENT OF cursor_name;
Want to change Customer Number 5155 to 5156
WHERE CURRENT OF:
When you use SQL you can update the current row by using
an UPDATE statement that includes a WHERE CURRENT
OF clause.
Changes made with this clause affect only the row on which
the cursor is positioned.
When a cursor is based on a join, only the table_name
specified in the UPDATE statement is modified.
Other tables participating in the cursor are not affected.
• The previous example only changed on line of the table
– Where CustomerNumber = 5155
• To change multiple rows we need to loop through the table and change
each row, one at a time.
• Need to use @@FETCH_STATUS
– Returns the status of the last cursor FETCH statement issued
against any cursor currently opened
– Also use a loop with BEGIN …FETCH….END
• WHILE @@FETCH_STATUS = 0
– This means that while the fetch statement is successful
– Then do the next line in the procedure
Return Value
Description
0
The FETCH statement was successful.
-1
The FETCH statement failed or the row was beyond the result set.
-2
The row fetched is missing.
Change multiple rows:
MORE COMPLEX PROCEDURE
CREATE TABLE AlphaLtd_product
(ProductName nVARCHAR(25) PRIMARY KEY,
ProductPrice NUMERIC(4,2),
QuantityOnHand NUMERIC(5,0),
LastStockDate DATETIME2)
CREATE TABLE AlphaLtd_purchase
(ProductName nVARCHAR(25),
Salesperson nVARCHAR(3),
PurchaseDate DATETIME2,
Quantity NUMERIC(4,2))
INSERT INTO AlphaLtd_product VALUES
('Small Widget',99,1,'2014-01-15');
INSERT INTO AlphaLtd_product VALUES
('Medium Wodget',75,1000,'2013-01-15');
INSERT INTO AlphaLtd_product VALUES
('Chrome Phoobar',50,100,'2014-01-15');
INSERT INTO AlphaLtd_product VALUES
('Round Chrome Snaphoo',25,10000, null);
INSERT INTO AlphaLtd_product VALUES
('Extra Huge Mega Phoobar +',9.95,1234,'2015-01-15');
INSERT INTO AlphaLtd_product VALUES
('Square Zinculator',45,1,'2013-12-31');
INSERT INTO AlphaLtd_product VALUES
('Anodized Framifier',49,5, NULL);
INSERT INTO AlphaLtd_product VALUES
('Red Snaphoo',1.95,10,'2012-12-31');
INSERT INTO AlphaLtd_product VALUES
('Blue Snaphoo',1.95,10,'2012-12-30');
INSERT INTO AlphaLtd_purchase VALUES
('Small Widget','CA','2014-07-14',1);
INSERT INTO AlphaLtd_purchase VALUES
('Medium Wodget','BB','2014-07-14',75);
INSERT INTO AlphaLtd_purchase VALUES
('Chrome Phoobar','GA','2014-07-14',2);
INSERT INTO AlphaLtd_purchase VALUES
('Small Widget','GA','2014-07-15',8);
INSERT INTO AlphaLtd_purchase VALUES
('Medium Wodget','LB','2014-07-15',20);
INSERT INTO AlphaLtd_purchase VALUES
('Round Chrome Snaphoo','CA','2014-07-16',5);
INSERT INTO AlphaLtd_purchase VALUES
('Small Widget','CA','2014-07-17',1);
THE CURSOR
SELECT
pur.Salesperson, pur.Quantity, prod.ProductPrice
FROM
AlphaLtd_purchase pur, AlphaLtd_product prod
WHERE pur.ProductName = prod.ProductName
ORDER BY Salesperson
DECLARE @NewSalesperson nVARCHAR(3),@OldSalesperson nVARCHAR(3)='xxx',
@QuantitySold NUMERIC(3),@ProductPrice NUMERIC(4),@TotalSale NUMERIC(6)=0,@Rate NUMERIC(3)=2
DECLARE @commission_cur as CURSOR
SET @commission_cur = CURSOR FOR
SELECT pur.Salesperson, pur.Quantity, prod.ProductPrice
FROM AlphaLtd_purchase pur, AlphaLtd_product prod
WHERE pur.ProductName=prod.ProductName
ORDER BY Salesperson
OPEN @commission_cur
FETCH NEXT FROM @commission_cur INTO @NewSalesperson,@QuantitySold,@ProductPrice
PRINT '*'
WHILE @@FETCH_STATUS = 0
BEGIN
IF @OldSalesperson = 'xxx'
--This statement only deals with the first record when @oldSalesperson = 'xxx'
BEGIN
SET @TotalSale = @TotalSale + (@QuantitySold * @ProductPrice)
SET @oldSalesperson = @NewSalesperson
FETCH NEXT FROM @commission_cur INTO @NewSalesperson,@QuantitySold,@ProductPrice
END
IF @OldSalesperson = @NewSalesperson
--This ststement deals with the second record onwards when @OldSalesperson = @NewSalesperson.
--Total sales are accumulated for each salesperson.
BEGIN
SET @TotalSale = @TotalSale + (@QuantitySold * @ProductPrice)
SET @oldSalesperson = @NewSalesperson
FETCH NEXT FROM @commission_cur INTO @NewSalesperson,@QuantitySold,@ProductPrice
END
IF @OldSalesperson <> @NewSalesperson
--This statement handles the flow when a different salesperson is encountered.
--i.e. @OldSalesperson <> @NewSalesperson
BEGIN
--The following prints out the total sale for the previous salesperson.
--CHAR(13) is a carriage return and CHAR(9) is an indent
PRINT 'Salesperson: ' + @OldSalesperson + CHAR(13) + CHAR(9)
--the next line will have a carriage return and be indented
+ 'Total Quantity Sold: ' + CONVERT(nVARCHAR(20),@TotalSale)+' units'+CHAR(13)+CHAR(9)
+ 'Commission - $' + CONVERT(nVARCHAR(20),CAST(@TotalSale*@Rate/100 as MONEY),1)
PRINT '***'
SET @TotalSale = 0
SET @TotalSale = @TotalSale + (@QuantitySold * @ProductPrice)
SET @oldSalesperson = @NewSalesperson
FETCH NEXT FROM @commission_cur INTO @NewSalesperson,@QuantitySold,@ProductPrice
END
END
--The while loop has now exited since the last record has already been fetched.
--The following prints out the commission for the last salesperson
PRINT 'Salesperson: ' + @OldSalesperson + CHAR(13) + CHAR(9)
+ 'Total Quantity Sold: ' + CONVERT(nVARCHAR(20),@TotalSale)+' units'+CHAR(13)+CHAR(9)
+ 'Commission - $' + CONVERT(nVARCHAR(20),CAST(@TotalSale*@Rate/100 as MONEY),1)
PRINT '*'
CLOSE commission_cur
DEALLOCATE commission_cur
Note the comment lines. They
help to follow the logic.
• The SELECT statement
• The FETCH commands
• The IF statements
Notice the carriage
returns and indents
Cursor in Cursor
The problem:
What are the courses, and the student number and names of the students who took
courses in semester 1 of 2008? The solution should look like the following.
The tables – used in SQL section
CREATE TABLE U_COURSES(
CourseNum NUMERIC(4),
CourseName nVARCHAR(8),
CourseDesc nVARCHAR(40),
CONSTRAINT CourseNum_pk PRIMARY KEY (CourseNum));
INSERT INTO U_COURSES VALUES
(1001, 'Actg1B10', 'Intro. to Accounting');
INSERT INTO U_COURSES VALUES
(1002, 'Fnce2G56', 'Intro. to Finance');
INSERT INTO U_COURSES VALUES
(1003, 'Actg2D17', 'Intermediate Accounting');
INSERT INTO U_COURSES VALUES
(1004, 'Actg4R43', 'Advanced Accounting');
INSERT INTO U_COURSES VALUES
(1005, 'Mktg2D24', 'Intro. to Marketing');
CREATE TABLE U_SECTIONS(
SectionId NUMERIC(5),
CourseNum NUMERIC(4)
CONSTRAINT CourseNum_fk REFERENCES U_COURSES,
SectionNum NUMERIC(2),
SemesterNum NUMERIC(6)
CONSTRAINT SemesterNum_fk REFERENCES U_SEMESTER,
FacNum NUMERIC(5)
CONSTRAINT FacNum_fk REFERENCES U_FACULTY,
CourseSecDay nVARCHAR(5),
CourseSecTime nVARCHAR(8),
LocNum NUMERIC(2)
CONSTRAINT LocNum2_fk REFERENCES U_CLASS_LOCATION,
CONSTRAINT SectionId_pk PRIMARY KEY (SectionId));
INSERT INTO U_SECTIONS VALUES
(10000,1001, 1, 200601, 3001, 'MWF', '10:00 AM', 35);
INSERT INTO U_SECTIONS VALUES
(10001,1001, 2, 200601, 3001, 'MWF', '3:00 PM', 35);
INSERT INTO U_SECTIONS VALUES
(10002,1002, 2, 200601, 3003, 'MTWRF', '11:00 AM', 55);
INSERT INTO U_SECTIONS VALUES
(10003,1003, 1,200702, 3004, 'MW', '9:00 AM', 45);
INSERT INTO U_SECTIONS VALUES
(10004,1003, 2, 200702, 3004, 'MW', '11:00 PM', 30);
INSERT INTO U_SECTIONS VALUES
(10005,1005, 1, 200702, 3006, 'T', '1:00 PM', 10);
INSERT INTO U_SECTIONS VALUES
(10006,1002, 1, 200703, 3002, 'W', '9:00 AM', 25);
INSERT INTO U_SECTIONS VALUES
(10007,1002, 2, 200703, 3002, 'R', '9:00 PM', 25);
INSERT INTO U_SECTIONS VALUES
(10008,1004, 1, 200703, 3005, 'MWF', '1:00 PM', 55);
INSERT INTO U_SECTIONS VALUES
(10009,1001, 1, 200701, 3001, 'MWF', '3:00 PM', 20);
INSERT INTO U_SECTIONS VALUES
(10010,1002, 1, 200701, 3006, 'MW', '3:00 PM', 40);
INSERT INTO U_SECTIONS VALUES
(10011,1002, 2, 200701, 3006, 'MW', '5:00 PM', 40);
INSERT INTO U_SECTIONS VALUES
(10012,1003, 1, 200801, 3003, 'W', '8:00 AM', 30);
INSERT INTO U_SECTIONS VALUES
(10013,1003, 2, 200801, 3003, 'W', '11:00 AM', 40);
INSERT INTO U_SECTIONS VALUES
(10014,1004, 1, 200801, 3005, 'MTWRF, '5:00 PM', 20);
The tables - continued
CREATE TABLE U_STUDENT(
StuNum NUMERIC(7),
StuLast nVARCHAR(20),
StuFirst nVARCHAR(10),
StuAddress nVARCHAR(40),
StuCity nVARCHAR(20),
StuProv nVARCHAR(3),
StuPostCode nVARCHAR(6),
StuYear nVARCHAR(2),
CONSTRAINT StuNum_pk PRIMARY KEY (StuNum));
INSERT INTO U_STUDENT VALUES
(2074567, 'Randolph', 'Jennifer', '156 Wendover Drive', 'Toronto', 'ONT', 'M3A1H6', 'SO');
INSERT INTO U_STUDENT VALUES
(2057612, 'Jameson', 'Philip', '812 Augustus Blvd.', 'Hamilton', 'ONT', 'L9B3S2', 'SR');
INSERT INTO U_STUDENT VALUES
(2087194, 'Smithers', 'Paula', '7135 Yonge Street', 'Toronto', 'ONT', 'M6H2T4', 'FR');
INSERT INTO U_STUDENT VALUES
(2062109, 'Gordon', 'Emily', '812 Augustus Blvd.', 'St. Catharines', 'ONT', 'L2S7D3', 'JR');
INSERT INTO U_STUDENT VALUES
(2059152, 'Anderson', 'Cynthia', '89 Ball Road', 'Toronto', 'ONT', 'M1J8R4', 'SR');
INSERT INTO U_STUDENT VALUES
(2061032, 'VanDyk', 'William', '452 Overlord Place', 'St. Catharines', 'ONT', 'L2S2K7', 'JR');
INSERT INTO U_STUDENT VALUES
(2075947, 'Brotherson', 'Stephanie', '5134 Main Street', 'Hamilton', 'ONT', 'L8T6Y2', 'SO');
INSERT INTO U_STUDENT VALUES
(2080034, 'Collins', 'Amanda', '645 Powerline Road', 'St. Catharines', 'ONT', 'L2S4R2', 'FR');
CREATE TABLE U_ENROLLMENT(
StuNum NUMERIC(7)
CONSTRAINT StuNum_fk REFERENCES U_STUDENT,
SectionId NUMERIC(5)
CONSTRAINT CourseNum2_fk REFERENCES
U_SECTIONS,
Mark NUMERIC(2),
Grade nVARCHAR(1),
CONSTRAINT StuSection_pk PRIMARY KEY (StuNum,
SectionId));
INSERT INTO U_ENROLLMENT VALUES
(2074567, 10000, 80, 'A');
INSERT INTO U_ENROLLMENT VALUES
(2061032, 10001, 75, 'B');
INSERT INTO U_ENROLLMENT VALUES
(2075947, 10002, 85, 'A');
INSERT INTO U_ENROLLMENT VALUES
(2059152, 10003, 70, 'B');
INSERT INTO U_ENROLLMENT VALUES
(2057612, 10004, 90, 'A');
INSERT INTO U_ENROLLMENT VALUES
(2061032, 10004, 78, 'B');
INSERT INTO U_ENROLLMENT VALUES
(2075947, 10005, 68, 'C');
INSERT INTO U_ENROLLMENT VALUES
(2062109, 10005, 88, 'A');
INSERT INTO U_ENROLLMENT VALUES
(2057612, 10006, 75, 'B');
INSERT INTO U_ENROLLMENT VALUES
(2087194, 10007,0,NULL);
INSERT INTO U_ENROLLMENT VALUES
(2080034, 10007,0,NULL);
INSERT INTO U_ENROLLMENT VALUES
(2059152, 10008,0,NULL);
INSERT INTO U_ENROLLMENT VALUES
(2061032, 10009,0,NULL);
INSERT INTO U_ENROLLMENT VALUES
(2057612, 10010, 78, 'B');
INSERT INTO U_ENROLLMENT VALUES
(2074567, 10011, 85, 'A');
INSERT INTO U_ENROLLMENT VALUES
(2075947, 10012, 80, 'A');
INSERT INTO U_ENROLLMENT VALUES
(2061032, 10013,0,NULL);
INSERT INTO U_ENROLLMENT VALUES
(2057612, 10013,0,NULL);
INSERT INTO U_ENROLLMENT VALUES
(2075947, 10014,0,NULL);
INSERT INTO U_ENROLLMENT VALUES
(2057612, 10014,0,NULL);
The First Cursor
SELECT US.SectionId, UC.CourseName, US.SectionNum
FROM U_COURSES UC, U_SECTIONS US
WHERE UC.CourseNum = US.CourseNum AND US.SemesterNum = 200801
ORDER BY US.SectionId, UC.CourseName, US.SectionNum;
The Second Cursor
SELECT UE.SectionId, UE.StuNum, UST.StuFirst, UST.StuLast
FROM U_ENROLLMENT UE, U_STUDENT UST, U_SECTIONS
US
WHERE UE.StuNum = UST.StuNum
AND UE.SectionId = US.SectionId AND US.SemesterNum = 200801
CREATE PROCEDURE NewUniversity_proc
AS
DECLARE
@x NUMERIC(5), @y nVARCHAR(8), @z NUMERIC(1),
@a NUMERIC(5), @b NUMERIC(7), @c nVARCHAR(10), @d nVARCHAR(20);
DECLARE @first_cur as CURSOR;
SET @first_cur = CURSOR FOR
SELECT US.SectionId, UC.CourseName, US.SectionNum
FROM U_COURSES UC, U_SECTIONS US
WHERE UC.CourseNum = US.CourseNum AND US.SemesterNum = 200801
ORDER BY US.SectionId, UC.CourseName, US.SectionNum;
OPEN @first_cur;
FETCH NEXT FROM @first_cur INTO @x, @y, @z;
WHILE @@FETCH_STATUS = 0 -- Outer cursor loop
BEGIN
DECLARE @second_cur as CURSOR;
SET @second_cur = CURSOR FOR
SELECT UE.SectionId, UE.StuNum, UST.StuFirst, UST.StuLast
FROM U_ENROLLMENT UE, U_STUDENT UST, U_SECTIONS US
WHERE UE.StuNum = UST.StuNum
AND UE.SectionId = US.SectionId AND US.SemesterNum = 200801
ORDER BY UE.SectionId, UE.StuNum;
-- Nested cursor
OPEN @second_cur;
FETCH NEXT FROM @second_cur into @a, @b, @c, @d;
PRINT @y + ' Section ' + CONVERT(nVARCHAR(20), @z)
PRINT '***'
WHILE @@FETCH_STATUS = 0 -- Inner cursor loop (nested cursor while)
BEGIN
If @x = @a
PRINT CONVERT(nVARCHAR(20), @b) + ' ' + @c + ' ' + @d;
FETCH NEXT FROM @second_cur into @a, @b, @c, @d;
END -- Inner cursor loop
PRINT '================================='
FETCH NEXT FROM @first_cur INTO @x, @y, @z;
CLOSE @second_cur;
DEALLOCATE @second_cur;
END -- Outer cursor loop
CLOSE @first_cur;
DEALLOCATE @first_cur;
Notice that the second cursor is
recreated each time you go through
the first cursor loop. This can
sometimes not be very efficient.
Exception Handling
• Exceptions
• Opportunity to issue meaningful error
messages
System Messages
• DIVIDE BY ZERO
• Two ways of showing a user information about an
error.
1. ERROR_NUMBER
2. ERROR_MESSAGE
All we are doing here is
forcing an error. The
actual error does not make
sense when it comes to
INSERTING values
Programmer-Defined Exceptions
• One can create their own conditions and names
• An example shown of how to define your own error
messages
• Life: Valid only for this block
Triggers
A database trigger is procedural code
Automatically executes in response to certain events on a particular on a particular or view in
a database.
The trigger is mostly used for maintaining the integrity of the information on the database.
An Example of a Login Trigger
Create Table master.dbo.audit_logins
(LoginName nVARCHAR(50),
-- holds the login name
LoginType nVARCHAR(50), -- holds the login type
LoginTime DATETIME2,
-- holds the time of the login
ClientHost nVARCHAR(50)) -- holds the host from which the login request originated
Create the Logon trigger:
Create TRIGGER TR_audit_logins
ON ALL SERVER WITH EXECUTE AS 'sa‘
FOR LOGON
AS
BEGIN
declare @LogonTriggerData xml
--XML datatype, stores XML data
set @LogonTriggerData = eventdata();
Insert into master..audit_logins
Select @LogonTriggerData.value('(/EVENT_INSTANCE/LoginName)[1]', 'varchar(50)'),
@LogonTriggerData.value('(/EVENT_INSTANCE/LoginType)[1]', 'varchar(50)'),
@LogonTriggerData.value('(/EVENT_INSTANCE/PostTime)[1]', 'datetime'),
@LogonTriggerData.value('(/EVENT_INSTANCE/ClientHost)[1]', 'varchar(50)')
END
Extensible Markup Language (XML) is a markup language that defines a set of rules for
encoding documents in a format that is both human-readable and machine-readable.
A markup language is a system for annotating a document in such a way that the syntax is
distinguishable from the text.
The design goals of XML emphasize simplicity, generality and usability across the Internet.
<recipe>
<title>Bread and Butter</title>
<ingredientslist>
<ingredient>Bread</ingredient>
<ingredient>Butter</ingredient>
</ingredientlist>
<preparation>
Put butter on a knife and spread on the bread.
</preparation>
</recipe>
What EVENT_INSTANCE contains the following data in XML
format
<EVENT_INSTANCE>
<EventType> event </EventType>
<PostTime> datetime </PostTime>
<SPID> spid </SPID>
<ClientHost> host </ClientHost>
<ServerName> name </ServerName>
<LoginName> login </LoginName>
<UserName> name </UserName>
<DatabaseName> name </DatabaseName>
<SchemaName> name </SchemaName>
<ObjectName> name </ObjectName>
<ObjectType> type </ObjectType>
<TSQLCommand> command </TSQLCommand>
</EVENT_INSTANCE>
Simple Trigger Examples
Will work with the FACTORY_WORKER table, used previously, and a
new table FACTORY_WORKER_BACKUP
CREATE TABLE FACTORY_WORKER
(FWNumber NUMERIC(4)
CONSTRAINT fw_pk primary key,
FWFirstName nVARCHAR(15),
FWLastName nVARCHAR(20),
FWRate NUMERIC(2))
CREATE TABLE FACTORY_WORKER_BACKUP
(FWNumber NUMERIC(4)
CONSTRAINT fw_backup_pk primary key,
FWFirstName nVARCHAR(15),
FWLastName nVARCHAR(20),
FWRate NUMERIC(2))
INSERT INTO FACTORY_WORKER VALUES
(5001,'Philip','Brown',5)
INSERT INTO FACTORY_WORKER VALUES
(5002,'Jane','Adler',6)
INSERT INTO FACTORY_WORKER VALUES
(5003,'Cheryl','Black',4)
INSERT INTO FACTORY_WORKER VALUES
(5004,'James','Newton',7)
INSERT INTO FACTORY_WORKER VALUES
(5005,'Sandra','Jones',6)
INSERT INTO FACTORY_WORKER_BACKUP
VALUES (5001,'Philip','Brown',5)
INSERT INTO FACTORY_WORKER_BACKUP
VALUES (5002,'Jane','Adler',6)
INSERT INTO FACTORY_WORKER_BACKUP
VALUES (5003,'Cheryl','Black',4)
INSERT INTO FACTORY_WORKER_BACKUP
VALUES (5004,'James','Newton',7)
INSERT INTO FACTORY_WORKER_BACKUP
VALUES (5005,'Sandra','Jones',6)
DML triggers execute when a user tries to modify data through a data manipulation language (DML)
event such as INSERT, UPDATE, or DELETE statements on a table or view.
DML triggers can be used to:
1. enforce business rules
2. enforce data integrity
3. query other tables.
Can include complex Transact-SQL statements. The trigger and the statement that fires it are treated as
a single transaction, which can be rolled back from within the trigger. If a severe error is detected (for
example, insufficient disk space), the entire transaction automatically rolls back.
The most common table-oriented triggers:
1. INSERT, DELETE, and UPDATE
2. AFTER INSERT, AFTER DELETE, AFTER UPDATE
3. INSTEAD OF.
Two special tables are used in trigger statements:
1.INSERTED:
•The inserted table stores copies of the affected rows during INSERT and UPDATE
statements.
•During an insert or update transaction, new rows are added simultaneously to both the
inserted table and the trigger table.
•The rows in the inserted table are copies of the new rows in the trigger table.
2.DELETED:
•The deleted table stores copies of the affected rows during DELETE and UPDATE
statements. During the execution of a DELETE or UPDATE statement, rows are deleted from
the trigger table and transferred to the deleted table.
•The deleted table and the trigger table ordinarily have no rows in common.
INSERT TRIGGER
CREATE TRIGGER trigAddFactoryWorker
ON FACTORY_WORKER
FOR INSERT
AS
DECLARE @FWNumber NUMERIC(4)
SELECT @FWNumber= (SELECT FWNumber FROM INSERTED)
PRINT 'FACTORY WORKER ' + CAST(@FWNumber as
nVARCHAR(20)) + ' IS ADDED.'
AFTER INSERT TRIGGER
CREATE TRIGGER trigAfterInsertFactoryWorker
ON FACTORY_WORKER
AFTER INSERT
AS
BEGIN
SET NOCOUNT ON
-- Stops the message indicating the number of rows affected by a Transact-SQL statement
-- from being returned as part of the results.
INSERT INTO FACTORY_WORKER_BACKUP
SELECT * FROM INSERTED
PRINT 'The Factory Worker Backup Table has been UPDATED.'
END
DELETE TRIGGER
CREATE TRIGGER trigDeleteFactoryWorker
ON FACTORY_WORKER
FOR DELETE
AS
DECLARE @FWNumber NUMERIC(4)
SELECT @FWNumber = (SELECT FWNumber FROM DELETED)
PRINT 'FACTORY WORKER ' + CAST(@FWNumber as
nVARCHAR(20)) + ' IS DELETED.'
AFTER DELETE TRIGGER
CREATE TRIGGER trigAfterDeleteFactoryWorker
ON FACTORY_WORKER
AFTER DELETE
AS
BEGIN
SET NOCOUNT ON
DELETE FROM FACTORY_WORKER_BACKUP
WHERE FWNumber = (SELECT FWNumber FROM DELETED)
PRINT 'The Factory Worker Backup Table has been UPDATED.'
END
UPDATE TRIGGER
CREATE TRIGGER trigUpdateFactoryWorker
ON FACTORY_WORKER
FOR UPDATE
AS
DECLARE @FWNumber NUMERIC(4)
SELECT @FWNumber = (SELECT FWNumber FROM INSERTED)
PRINT 'FACTORY WORKER ' + CAST(@FWNumber as nVARCHAR(20)) + ' IS
UPDATED.'
AFTER UPDATE TRIGGER
CREATE TRIGGER trigAfterUpdateFactoryWorker
ON FACTORY_WORKER
AFTER UPDATE
AS
BEGIN
DECLARE @FWNumber NUMERIC(4), @FWFirstName nVARCHAR(20), @FWLastName nVARCHAR(20)
SET NOCOUNT ON
SELECT @FWNumber = (SELECT FWNumber FROM INSERTED)
SELECT @FWFirstName = (SELECT FWFirstName FROM INSERTED)
SELECT @FWLastName = (SELECT FWLastName FROM INSERTED)
UPDATE FACTORY_WORKER_BACKUP
SET FWNumber = @FWNumber WHERE FWNumber = @FWNumber
UPDATE FACTORY_WORKER_BACKUP
SET FWFirstName = @FWFirstName WHERE FWNumber = @FWNumber
UPDATE FACTORY_WORKER_BACKUP
SET FWLastName = @FWLastName WHERE FWNumber = @FWNumber
PRINT 'The Factory Woker Backup Table has been UPDATED.'
END
INSTEAD OF TRIGGER
CREATE TRIGGER trigInsteadOfFactoryWorker
ON FACTORY_WORKER
INSTEAD OF UPDATE
AS
BEGIN
SET NOCOUNT ON
IF UPDATE (FWNumber)
RAISERROR ('You cannot change a Factory Worker Number!
This transaction will not be entered.',10,1)
END