Download Oracle PL/SQL

Oracle PL/SQL
Eyad Husni Elshami
Why PL/SQL
• Block Structures:
– PL/SQL consists of blocks of code, which can be nested within each
other. Each block forms a unit of a task or a logical module. PL/SQL
Blocks can be stored in the database and reused.
•
Procedural Language Capability:
– PL/SQL consists of procedural language constructs such as conditional
statements (if else statements) and loops like (FOR loops).
•
Better Performance:
– PL/SQL engine processes multiple SQL statements simultaneously as a
single block, thereby reducing network traffic.
• Error Handling:
– PL/SQL handles errors or exceptions effectively during the execution of
a PL/SQL program. Once an exception is caught, specific actions can be
taken depending upon the type of the exception or it can be displayed
to the user with a message.
Basic Structure of PL/SQL
DECLARE
/* Declarative section: variables, types, and local subprograms. It is an
optional section*/
BEGIN
/* Executable section: procedural and SQL statements go here. */
/* This is the only section of the block that is required. It is an
mandatorysection */
EXCEPTION
/* Exception handling section: error handling statements go here. It is an
optional section */
END;
PL/SQL Variables and Types
• Information is transmitted between a PL/SQL
program and the database through variables.
Every variable has a specific type associated
with it. That type can be one of the types used
by SQL for database columns.
– A generic type used in PL/SQL such as NUMBER,
CHAR, DATE, …etc
– Declared to be the same as the type of some
database column
PL/SQL Variables and Types
Declar
Std_id number(2);
Std_name Students.sname%TYPE;
Std_record Students%ROWTYPE;
Begin
select sid into std_id from students where sname=‘ALI’;
select sname into std_name from students where sid=12345;
select * into std_record from students where sid=12345;
End
PL/SQL Control Structures
• Conditional statement:
– IF Statement
• Iterative Statements:
– Simple Loop
– While Loop
– For Loop
PL/SQL Conditional statement
IF condition THEN
Statements
ELSIF condition THEN
Statements
ELSE
Statements
END IF;
Declare
day char(3):= to_char(sysdate,'DY');
Begin
If day = 'FRI' then
DBMS_OUTPUT.PUT_LINE('Week
end');
Elsif day = 'SAT' then
DBMS_OUTPUT.PUT_LINE('New
work week');
Else
DBMS_OUTPUT.PUT_LINE('have a
nice day');
End if;
End;
/
PL/SQL Iterative Statements
Simple loop syntax:
DECLARE
i NUMBER := 1;
LOOP
<loop_body> ;
EXIT; /* EXIT WHEN condition;*/
BEGIN
LOOP
INSERT INTO T1 VALUES(i,i);
i := i+1;
EXIT WHEN i>100;
END LOOP;
END LOOP;
END;
PL/SQL Iterative Statements
While loop syntax:
DECLARE
i NUMBER := 1;
WHILE condition LOOP
< loop_body> ;
END LOOP;
BEGIN
WHILE i<100 LOOP
INSERT INTO T1
VALUES(i,i);
i := i+1;
END LOOP;
END;
PL/SQL Iterative Statements
For loop syntax:
DECLARE
i NUMBER := 1;
FOR counter IN
val1..val2 LOOP
< loop_body> ;
END LOOP;
BEGIN
FOR i IN 1..100 LOOP
INSERT INTO T1
VALUES(i,i);
END LOOP;
END;
PL/SQL Cursors
• What are Cursors?
– A cursor is a temporary work area created in the
system memory when a SQL statement is executed.
– A cursor contains information on a select statement
and the rows of data accessed by it. This temporary
work area is used to store the data retrieved from the
database, and manipulate this data.
– A cursor can hold more than one row, but can process
only one row at a time. The set of rows the cursor
holds is called the active set.
PL/SQL Implicit Cursors:
• When you execute DML statements or SELECT
statements, implicit cursors are created to process
these statements, there are attributes for each cursor:
– %FOUND:
• Return TRUE value if DML statement affect at least one row or the
select statement return at least on (example SQL%FOUND)
– %NOTFOUND:
• Return FLASE value if DML statement affect at least one row or the
select statement return at least on (example SQL%NOTFOUND)
– %ROWCOUNT:
• Return the number of rows affected by the DML/SELECT statement
(example SQL%ROWCOUNT)
– %ISOPEN:
• Return TRUE value if the cursor is already open in the program.
PL/SQL Implicit Cursors:
DECLARE
rows_count number(5);
BEGIN
UPDATE students SET saverage= 40
where saverage is null ;
IF SQL%NOTFOUND THEN
dbms_output.put_line('None of the averages where updated');
ELSIF SQL%FOUND THEN
rows_count := SQL%ROWCOUNT;
dbms_output.put_line(‘Averages for ' || rows_count|| ‘ students
are updated');
END IF;
END;
PL/SQL Explicit Cursors
• An explicit cursor is defined in the declaration
section of the PL/SQL Block. It is created on a
SELECT Statement which returns more than one
row .
• There are four steps in using an Explicit Cursor.
– DECLARE the cursor in the declaration section.
– OPEN the cursor in the Execution Section.
– FETCH the data from cursor into PL/SQL variables or
records in the Execution Section.
– CLOSE the cursor in the Execution Section before you
end the PL/SQL Block.
PL/SQL Explicit Cursors
DECLARE
CURSOR std_cur IS
SELECT sid, sname, saverage FROM students;
std_rec std_cur%rowtype;
BEGIN
IF NOT std_cur%ISOPEN THEN
OPEN std_cur;
END IF;
LOOP
FETCH std_cur INTO std_rec;
EXIT WHEN std_cur%NOTFOUND;
dbms_output.put_line(std_rec.sid || ' ' ||std_rec.sname || '
||std_rec.saverage+5);
END LOOP;
END;
'
PL/SQL Procedures
• A stored procedure or in simple a procedure is a
named PL/SQL block which performs one or more
specific task.
• This is similar to a procedure in other programming
languages.
• A procedure is similar to an anonymous PL/SQL Block
but it is named for repeated usage.
• We can pass parameters to procedures in three ways:
1) IN-parameters
2) OUT-parameters
3) IN OUT-parameters
PL/SQL Procedures
CREATE OR REPLACE PROCEDURE update_name IS
BEGIN
UPDATE students
SET sname = UPPER(sname);
UPDATE collge
SET cname = UPPER(cname);
COMMIT;
END;
PL/SQL Procedures
CREATE OR REPLACE PROCEDURE upadet_average
(push_value IN NUMBER) IS
BEGIN
UPDATE students
SET saverage = saverage +push_value
WHERE saverage BETWEEN 55 and 59;
COMMIT;
END;
PL/SQL Procedures
CREATE OR REPLACE PROCEDURE student_details IS
CURSOR std_cur IS
SELECT sname, cid, saverage FROM students;
std_rec std_cur%rowtype;
BEGIN
FOR std_rec in std_cur LOOP
dbms_output.put_line(std_cur.sname || ' ' ||std_cur.cid|| '
' ||std_cur.saverage);
END LOOP;
END;
PL/SQL Procedures
Execute procedurename;
PL/SQL Functions
• A function is a named PL/SQL Block which is
similar to a procedure. The major difference
between a procedure and a function is, a
function must always return a value, but a
procedure may or may not return a value.
PL/SQL Functions
CREATE OR REPLACE FUNCTION need_to_pass (std_id IN NUMBER)
RETURN NUMBER
IS
point NUMBER;
BEGIN
SELECT SAVERAGE INTO point
FROM students
WHERE sid = std_id;
IF (point<60) THEN
RETURN (60-point);
ELSE
RETURN 0;
END IF;
END;
PL/SQL Functions
• Execution for function like:
1. Since a function returns a value we can assign it
to a variable.
X := need_to_pass(12345);
2. As a part of a SELECT statement
SELECT sname,saverage, need_to_pass(sid)
FROM STUDENTS;
3. In a PL/SQL Statements like,
dbms_output.put_line(need_to_pass(sid));
PL/SQL Triggers
• A trigger is a pl/sql block structure which is fired when
a DML statements like Insert, Delete, Update is
executed on a database table.
CREATE OR REPLACE TRIGGER trigger_name
{BEFORE | AFTER | INSTEAD OF }
{INSERT | UPDATE | DELETE}
[OF col_name] ON table_name
[REFERENCING OLD AS o NEW AS n]
[FOR EACH ROW]
WHEN (condition)
BEGIN
--- sql statements
END;
PL/SQL Triggers
CREATE or REPLACE TRIGGER saverage_history
BEFORE UPDATE OF saverage ON stdudents
FOR EACH ROW /* WHEN :new.saverage>90*/
BEGIN
INSERT INTO archive_average VALUES (:old.sid,
:old.saverage, :new.saverage, sysdate, user);
END;
PL/SQL Exception Handling
We’ll study it later
create function grade(stdid in number) return char
is
savg stduents.saverage%type;
Begin
select saverage into asvg from stduents
where sid= stdid;
if savg>=65 then
return 'A‘;
Else
Return ‘B’;
End if;
End;