PL/SQL
Chapter 8PL/SQLOutlineProceduresCursorsTriggers
Procedural SQLSQL does not support the conditional execution of
procedures as well as looping operations. To overcome the lack of
procedural functionality in SQL and to provide standardization,
SQL-99 standard defines the use of persistent stored modules
(PSM).
What is PSM?A PSM is a block of code containing standard SQL
statements and procedural extensions that is stored and executed at
the DBMS server.The PSM represents business logic that can be
encapsulated, stored and shared among multiple database
users.Oracle implements PSMs through its procedural SQL
language.What is PL/SQL and where can PL/SQL be used?Procedural SQL
(PL/SQL) is a language that makes it possible to use and store
procedural code and SQL statements within the database and merge
SQL and traditional programming constructs. The procedural code is
executed as a unit by the DBMS when it is invoked b the end
user.PL/SQL is used to create Anonymous PL/SQL blocks (without
name)Stored ProceduresPL/SQL functionsTriggers
PL/SQL blockThe PL/SQL block starts with the DECLARE section in
which the variables, the data types or the initial values are
declared.The PL/SQL block ends with the word ENDThe PL/SQL block
can be executed by typing / and press enter key.Each statement
inside the PL/SQL code must end with a semicolon ;.To display the
output use the command dbms_output.put_line(any
string);.Conditional statement or Looping statements can be used
after declare statements;The SELECT statement uses the INTO keyword
inside the PL/SQL block of code to assign the output of the query
to a PL/SQL variable. If the SELECT statement returns more than one
value, you will get an error.7PL/SQL Program Blocks
8Commands included in PL/SQLComments: PL/SQL program includes
commands such as Comments statements that are lines of text that
explain or document a program step or series of steps.Not executed
by interpreterTo create a block of comments enclosed between /* and
*/ To create one line comment type two hyphens -- at the beginning
of the line.PL/SQL programs have Commands to perform arithmetic
operationsAssignment statements that assign values to
variablesConditional structures to perform decisionsLooping
structures to repeat instructions multiple timesSQL commands that
retrieve data.
Procedural StatementsSequencesStatement 1;Statement 2;Control
StatementsIF THEN statement1;ELSE statement2;ENDID;Looping
StructuresDO WHILE LOOP. Statement 1; Statement
2;ENDLOOP10Assignment StatementsAssigns a value to a variableAn
assignment statement has the following syntaxvariable_name :=
value;Value can be a literal:current_s_first_name := 'John';Value
can be another variable:current_s_first_name :=
s_first_name;11Displaying PL/SQL Program Output in SQL*PlusPL/SQL
output bufferMemory area on database server Stores programs output
values before they are displayed to userShould increase the size of
the buffer asSET SERVEROUTPUT ON SIZE buffer_sizeDefault buffer
size 2000 bytesTo display more than just a few lines of output, it
is better to make the output buffer larger than the default
size.Maximum is 1000000 bytes 12Displaying PL/SQL Program Output in
SQL*Plus (continued)Display program
outputDBMS_OUTPUT.PUT_LINE('display_text');The display_text value
can contain literal character strings such as My name is Roohi or
variable names such as current_s_first.Display maximum of 255
characters of text data13Executing a PL/SQL Program in
SQL*PlusCreate program in text editorCopy and paste program
commands into SQL*Plus windowPress Enter after last program
commandType front slash ( / )Then press Enter again
14Executing a PL/SQL Program in SQL*PlusDECLARE todays_date
DATE; X number;BEGIN
todays_date := SYSDATE;X:= 1; DBMS_OUTPUT.PUT_LINE('Today''s
date is ');
DBMS_OUTPUT.PUT_LINE(todays_date);DBMS_OUTPUT.PUT_LINE(x);
END;
Write a PL/SQL program to display the current date as shown
below Todays date is 27-Feb-2012A Guide to Oracle10g15PL/SQL Data
Conversion FunctionsSometimes the PL/SQL interpreter is unable to
implicitly convert value and an error occurs.Other times, PL/SQL
interpreter performs an implicit conversion and produce
unexpected/invalid dataExplicit data conversionsConvert variables
to different data types using data conversion functions that are
built into PL/SQL.
16Display todays date using concatenated character stringTo
concatenate two strings in PL/SQL, you use the double bar (||)
operator:new_string := string1 || string2;
SQL> DECLARE 2 todays_date DATE; 3 BEGIN 4 todays_date
:=SYSDATE; 5 DBMS_OUTPUT.PUT_LINE('Today''s date is ' ||
TO_CHAR(todays_date)); 6 END; 7 /
PL/SQL procedure successfully completed.17PL/SQL Decision
Control StructuresUse IF/THEN/ELSE to execute code if condition is
true or FALSEIF condition THEN commands that execute if condition
is TRUE; ELSE commands that execute if condition is FALSE; END
IF;
Evaluates ELSE commands if condition is FALSE18PL/SQL Decision
Control StructuresUse IF/ELSIF decision control structure to test
for many different conditions.:IF condition1 THEN commands that
execute if condition1 is TRUE; ELSIF condition2 THEN commands that
execute if condition2 is TRUE; ELSIF condition3 THEN commands that
execute if condition3 is TRUE; ... ELSE commands that execute if
none of the conditions are TRUE; END IF;19LoopsPL/SQL has 5 loop
structuresLOOPEXIT WHENWHILE ..LOOPNumeric FOR loops
20The LOOP...EXIT WHEN LoopThe LOOPEXITWHEN loop can also be
either a pretest or a post test loop.LOOP program statements EXIT
WHEN condition;END LOOP;
21The WHILE...LOOPThe WHILE.LOOP is a pretest loop that
evaluates the exit condition before it executes any program
statement.
WHILE condition LOOP program statementsEND LOOP;
22The Numeric FOR LoopDoes not require explicit counter
incrementThe loop counter variable and it start and end values are
declared in the loops FOR statement.Automatically increments
counter variable until it reaches the end value.
FOR counter_variable IN start_value .. end_valueLOOP program
statementsEND LOOP;
23Using SQL Queries in PL/SQL ProgramsAction queries can be used
as in SQL*Plus
May use variables in action queries
DDL commands may not be used in PL/SQL24Using SQL Commands in
PL/SQL Programs
Okay that slide title is figure caption and not heading?PL/SQL
block to insert a new row in the VENDOR tableSET SERVEROUTPUT
ONBEGIN INSERT INTO VENDORVALUES (25772,Clue Store, Issac Hayes,
456, 323-2009, VA, N); DBMS.OUTPUT.PUT_LINE(New Vendor Added);END;/
-- to execute An anonymous PL/SQL ProgramPL/SQL block to count the
number of products having different price rangesDECLAREW_P1
NUMBER(3) := 0;W_p2 number(3) := 10;W_P1 NUMBER(2) := 0;BEGINWHILE
W_P2 = P_MIN*2; DBMS_OUTPUT.PUT_LINE ('* * Update finished *
*');END;
STORED PROCEDURESTo execute the stored procedure, use the
followijg syntax:EXEC procedure_name[(paramenter_list)]
Create a procedure to assign an additional percent discount (an
input variable) for all products when the quantity on Hand is more
than or equal to twice the minimum quantity.CREATE OR REPLACE
PROCEDURE PRC_PROD_DISCOUNT(WPI IN NUMBER) ASBEGIN IF ((WPI = 1))
THEN -- validate WPI parameter DBMS_OUTPUT.PUT_LINE('Error: Value
must be greater than 0 and less than 1'); ELSE -- if value is
greater than 0 and less than 1UPDATE PRODUCT SET P_DISCOUNT =
P_DISCOUNT + WPI WHERE P_QOH >= P_MIN*2;DBMS_OUTPUT.PUT_LINE ('*
* Update finished * *'); END IF;END;
Run the ProcedureEXEC PRC_PROD_DISCOUNT (1.5);What is the
outcome?EXEC PRC_PROD_DISCOUNT (.05);What is the outcome?
33Oracle SequencesMS Access AutoNumber data type fills a column
with unique numeric valuesOracle sequencesIndependent object in the
databaseNamed, used anywhere a value expectedNot tied to a table or
columnGenerate numeric values that can be assigned to any column in
any tableCreated and deleted at any time
34Create a procedure which adds a new invoice.CREATE OR REPLACE
PROCEDURE PRC_INV_ADD (W_CUS_CODE IN VARCHAR2, W_DATE IN DATE)AS
BEGIN INSERT INTO INVOICE VALUES(INV_NUMBER_SEQ.NEXTVAL,
W_CUS_CODE, W_DATE); DBMS_OUTPUT.PUT_LINE('Invoice added');END;
Create a procedure to add a new customerCREATE OR REPLACE
PROCEDURE PRC_CUS_ADD(W_LN IN VARCHAR, W_FN IN VARCHAR, W_INIT IN
VARCHAR, W_AC IN VARCHAR, W_PH IN VARCHAR)AS BEGIN-- note that the
procedure uses the CUS_CODE_SEQ sequence created earlier. Attribute
names are required when not giving values for all table attributes
INSERT INTO CUSTOMER(CUS_CODE,CUS_LNAME, CUS_FNAME, CUS_INITIAL,
CUS_AREACODE, CUS_PHONE) VALUES (CUS_CODE_SEQ.NEXTVAL, W_LN, W_FN,
W_INIT, W_AC, W_PH); DBMS_OUTPUT.PUT_LINE ('Customer ' || W_LN ||
', ' || W_FN || ' added.');END;/EXEC PRC_CUS_ADD(Walker,
James,NULL, 615, 84-HORSE);The result isCustomer Walker, James
added.PL/SQL procedure successfully completed.
Create a procedure which adds a new product line row for a given
invoice.CREATE OR REPLACE PROCEDURE PRC_LINE_ADD (W_LN IN NUMBER,
W_P_CODE IN VARCHAR2, W_LU NUMBER)AS W_LP NUMBER := 0.00;BEGIN --
GET THE PRODUCT PRICESELECT P_PRICE INTO W_LP FROM PRODUCT WHERE
P_CODE = W_P_CODE;
-- ADDS THE NEW LINE ROW INSERT INTO LINE
VALUES(INV_NUMBER_SEQ.CURRVAL, W_LN, W_P_CODE, W_LU,
W_LP,null);
DBMS_OUTPUT.PUT_LINE('Invoice line ' || W_LN || '
added');END;
In order to insert a new record in the LINE table, we need to
know the Invoice Number, Product Code, Line Units (the values are
obtained from the input parameters), Line Price ( the value is
obtained from the Product Price i.e. p_price) in a PRODUCT
TableCursorA cursor is a special construct in procedural SQL to
hold the data rows returned by an SQL query. A cursor is a reserved
area of memory in which the output of the query is stored like an
array holding columns and rows.Cursors are held in a reserved
memory area in the DBMS server, not in the client computer.CursorsA
cursor is a pointer to a memory location on database server that
the DBMS uses to process a SQL queryCursors are used to retrieve
and manipulate database data in PL/SQL
programsTypes:ImplicitExplicit
Implicit Cursor
Implicit CursorsContext areaA memory location on the database
serverContains information about query e.g. no. of rows that the
query processes, and a machine language representation of the query
etc.Created by INSERT, UPDATE, DELETE, or SELECTActive setFor
SELECT queries, the context area also stores the active set, which
is the set of data rows that query retrievesImplicit cursor is a
pointer to the context areaFor Implicit cursor, there is no need to
write commands explicitly to create it or retrieve its
value.Implicit CursorsExecuting a SELECT query creates an implicit
cursor i.e. Implicit cursor can be used to assign the output of a
SELECT query to PL/SQL program variables when we are sure that the
query will return one and only one record.If the query returns more
than one record, or does not return any record, an error
occurs.Using an Implicit CursorTo retrieve data values from a
querys implicit cursor into PL/SQL program variables add INTO
clause : SELECT field1, field2, ...INTO variable1, variable2,
...FROM table1, table2, ...WHERE join_ conditionsAND
search_condition_to_retrieve_1_record;The variables must have been
declared in the programs declaration sectionThe variables must have
the same data types as the associated database fields.Reference
VariablesReference variables directly reference specific database
field or record and assume data type of the associated field or
record%TYPE: is a reference data type which assumes the data type
of a database fielddata declaration syntax:variable_name
tablename.fieldname%TYPE;e.g. current_c_last
Customer.Cus_Lname%TYPE;The current_c_last variable would assume a
data type of VARCHAR2(15), because this is the data type of
Cus_Lname field in the CUSTOMER tableImplicit Cursors
(continued)Useful to use %TYPE reference data type to declare
variables used with implicit cursorsvariable_name
tablename.fieldname%TYPEe.g. current_c_last
customer.cus_lname%TYPEVariable nameTable nameField name in the
tableReference Variables%ROWTYPE: is a reference data type which
assumes the data type of a database recorddata declaration
syntax:row_variable_name tablename%ROWTYPE;e.g. customer_row
Customer%ROWTYPE;The CUSTOMER_ROW references all of the fields in
the CUSTOMER TABLE, and each field has the same data type as its
associated database fields.
Reference VariablesHow do you refer to individual data field
within a %ROWTYPE variable?Use the syntax
row_variable_name.fieldnameIf u have to refer to f_first name, you
can write customer_row.cus_fnameor the balance, you can
writecustomer_row.cus_balanceReference Data Type used with
Cursors%TYPE: is a reference data type which assumes the data type
of a database fielddata declaration syntax:variable_name
Cursor_Name.fieldname%TYPE;
e.g. current_c_last cus_cursor.cus_fname%TYPE;%ROWTYPE: is a
reference data type which assumes the data type of a database
recorddata declaration syntax:variable_name
Cursor_Name%ROWTYPE;
e.g. customer_row cus_cursor%ROWTYPE;
SQL> DECLARE 2 current_c_last customer.cus_lname%TYPE; 3
current_c_first customer.cus_fname%TYPE; 4 BEGIN 5 SELECT
cus_lname, cus_fname 6 INTO current_C_last, current_C_first 7 FROM
customer 8 WHERE cus_code = 10010; 9 DBMS_OUTPUT.PUT_LINE(' The
customer ''s name is ' || current_f_first || ' ' ||
current_f_last); 10 END; 11 /The customer's name is Ramas
Alfred
PL/SQL procedure successfully completed.PL/SQL program that
displays last name and first name from the CUSTROMER table where
cus_code =10010 using an implicit cursorSQL> DECLARE 2
current_c_last customer.cus_lname%TYPE; 3 current_c_first
customer.cus_fname%TYPE; 4 BEGIN 5 SELECT cus_lname, cus_fname 6
INTO current_f_last, current_f_first 7 FROM customer 8 WHERE
cus_lname LIKE S%; 9 DBMS_OUTPUT.PUT_LINE(' The customer ''s name
is ' || current_f_first || ' ' || current_f_last); 10 END; 11 /
DECLARE*ERROR at line 1:ORA-01422: exact fetch returns more than
requested number of rowsORA-06512: at line 8Error ORA-01422: exact
fetch returns more than requested number of rows Implicit cursor
query tried to retrieve multiple recordsWhen implicit cursor query
returns no recordsSQL> DECLARE 2 current_c_last
customer.cus_lname%TYPE; 3 current_c_first customer.cus_fname%TYPE;
4 BEGIN 5 SELECT cus_lname, cus_fname 6 INTO current_f_last,
current_f_first 7 FROM customer 8 WHERE cus_code= 12345; 9
DBMS_OUTPUT.PUT_LINE(' The customer ''s name is ' ||
current_f_first || ' ' || current_f_last); 10 END; 11
/DECLARE*ERROR at line 1:ORA-01403: no data foundORA-06512: at line
5Explicit CursorsExplicit cursors are created to retrieve and
display data in PL/SQL programs for query that might Retrieve
multiple recordsReturn no records at allExplicit cursors must be
explicitly declared in the programs declaration sectionExplicit
commands are written to process the cursor.Steps for creating and
using explicit cursorDeclare cursorOpen cursorFetch data rowsClose
cursorUsing an Explicit CursorDeclaring an Explicit CursorBy
declaring an EC, a memory location is created on the database
server that processes query and stores the records that the query
retrievesCURSOR cursor_name IS select_query;Cursor_name can be any
valid PL/SQL variable name.Select_query is the query that retrieves
the desired data value ( simple, complex , nested query etc.)The
querys search condition can contain PL/SQL variables as long as the
variables are declared before the cursor is declared and are
assigned values before the program opens and processes the
cursor.Using an Explicit CursorOpen the cursorOPEN cursor_name;When
the open command is executed, the PL/SQL interpreter examines or
parses the cursors SQL query, confirms that the query contains no
syntax errors and translates the query into a machine language
format.The system stores the parsed query in the cursors context
area and creates the memory structure that will store the active
set.The cursor does not retrieve the data values at this stage.
Using an Explicit CursorFetching the data rowsLOOP FETCH
cursor_name INTO variable_name(s); EXIT WHEN
cursor_name%NOTFOUND;It retrieves the query data from the database
into the active set, one row at a time.The FETCH command associates
each field value with a program variable.The FETCH command is
executed within a loop in order for the query to return several
records.The cursor variable or variables are declared using either
the %TYPE or %ROWTYPE reference data type.Using an Explicit
CursorActive set pointerIt is a pointer that indicates the memory
location of next record that is retrieved from databaseWhen the
FETCH command executes past the last record of the query, the
active set pointer points an empty record.The exit condition
cursor_name%NOTFOUND determines whether the last cursor record has
been fetched by checking if the active pointer is pointing to the
last record and then the loop exits.Closing the cursorClose the
cursor after it processes all of the records in the active set so
that its memory area and resources are available to the system for
other tasks. CLOSE cursor_name;The system automatically closes the
cursor when the program that processes the cursor ends.
Explicit Cursor with %TYPEIt is used when a cursor retrieves one
data field.
Using cursors create a procedure that lists all products that
have a quantity on hand greater than the average quantity on hand
for all products.
CREATE OR REPLACE PROCEDURE PRC_CURSOR_EXAMPLE
ISW_P_CODEPRODUCT.P_CODE%TYPE;W_P_DESCRIPTPRODUCT.P_DESCRIPT%TYPE;--W_TOTNUMBER(3);
CURSOR PROD_CURSOR IS SELECT P_CODE, P_DESCRIPT FROM PRODUCT
WHERE P_QOH > (SELECT AVG(P_QOH) FROM
PRODUCT);BEGINDBMS_OUTPUT.PUT_LINE('PRODUCTS WITH P_QOH >
AVG(P_QOH)');
DBMS_OUTPUT.PUT_LINE('======================================');OPEN
PROD_CURSOR;LOOP FETCH PROD_CURSOR INTO W_P_CODE, W_P_DESCRIPT;
EXIT WHEN PROD_CURSOR%NOTFOUND; DBMS_OUTPUT.PUT_LINE(W_P_CODE ||'
-> ' || W_P_DESCRIPT );END LOOP;
DBMS_OUTPUT.PUT_LINE('======================================');DBMS_OUTPUT.PUT_LINE('TOTAL
PRODUCT PROCESSED ' || PROD_CURSOR%ROWCOUNT);
DBMS_OUTPUT.PUT_LINE('--- END OF REPORT ----');
CLOSE PROD_CURSOR;END;/
Write a program that uses an Explicit Cursor to retrieve and
display the invoice number value (using %TYPE variable) for every
record in the INVOICE table for the customer code 10014.DECLARE
current_cus_code NUMBER(4); CURSOR invoice_cursor IS SELECT
inv_number FROM invoice WHERE inv_number = current_cus_code;
current_inv invoice.inv_number%TYPE;BEGIN
OPEN invoice_cursor; current_inv_num :=
1001';DBMS_OUTPUT.PUT_LINE('The current invoice number for ' ||
current_cus_code || are as follows); LOOP FETCH invoice_cursor INTO
current_inv; EXIT WHEN invoice_cursor%NOTFOUND;
DBMS_OUTPUT.PUT_LINE(current_nv); END LOOP; CLOSE
invoice_cursor;END;/
Explicit Cursor with %ROWTYPEIt is used when a cursor retrieves
multiple data fields.Use a single variable that has %ROWTYPE
reference data typeAssume the same data type as the row that the
cursor retrieves.How to declare a cursor %ROWTYPE
variablerow_variable_name cursor_name%ROWTYPE
e.g. customer_row location_cursor%ROWTYPETo reference individual
data fields within a %ROWTYPE variable,
userow_variable_name.fieldnamee.g. customer_row.room to reference
the ROOM field in the location_row variable.Write a program that
uses an Explicit Cursor to retrieve and display the invoice number
value (using %TYPE variable) for every record in the INVOICE table
in which the customer code is 10014.DECLARE current_inv_num
NUMBER(4); CURSOR invoice_cursor IS SELECT p_code FROM invoice
WHERE inv_number = current_inv_num; current_p_code
invoice_cursor%ROWTYPE;BEGIN
OPEN invoice_cursor; current_inv_num := 1001'; LOOP FETCH
invoice_cursor INTO invoice_cursor; EXIT WHEN
invoice_cursor%NOTFOUND; DBMS_OUTPUT.PUT_LINE('The current product
code in ' || current_inv_num || ' ' || invoice_p_code.p_code); END
LOOP; CLOSE invoice_cursor;END;/
TriggersA Trigger is procedural SQL code that is automatically
invoked by the RDBMS upon the occurrence of a given data
manipulation event.A trigger is invoked before or after a data row
is actually inserted, updated or deleted.A trigger is associated
within a database table.Each database table may have one or more
triggers.A trigger is executed as part of the transaction that
triggered it.Uses of TriggersTriggers can be used to enforce
constraints that cannot be enforced at the DBMS design and
implementation levels.Triggers add functionality by automating
critical actions and providing appropriate warnings and suggestions
for remedial action.Triggers can be used to update table values,
insert records in tables and call other stored procedures.Syntax to
create a Trigger in OracleCREATE OR REPLACE TRIGGER
trigger_name[BEFORE/AFTER] [DELETE/ INSERT/ UPDATE OF column_name]
ON table_name[FOR EACH ROW][DECLARE][varaible_namedata
type[:=initial_value] ]BEGIN PL/SQL instructions; .END;Syntax to
create a Trigger in OracleThe Triggering timing: BEFORE or AFTER.
This timing indicates when the triggers PL/SQL code executes; in
this case, before or after the triggering statement is completed.
(BEFORE means before the changes are permanently saved to disk but
after the changes are made in memory.)
The triggering event: the statement that causes the trigger to
execute (INSERT, UPDATE or DELETE).The triggering level: A
statement-level trigger is assumed if we omit the FOR EACH ROW
keywords. This executes only once before or after the triggering
statement is completed.A row-level trigger requires use of the FOR
EACH ROW keywords. This is executed once for reach row affected by
the triggering statement.The Triggering action: The PL/SQL code
enclosed between the BEGIN and END keywords. Each statement inside
the PL/SQL code must end with a semicolon.ExampleCreate a trigger
which should be activated when a products quantity on hand is
updated when the product is sold, the system should automatically
check whether the quantity on hand falls below its minimum
allowable quantity.
CREATE OR REPLACE TRIGGER TRG_PRODUCT_REORDERAFTER INSERT OR
UPDATE OF P_QOH ON PRODUCTBEGIN UPDATE PRODUCTSET P_REORDER = 1
WHER P_QOH
