CIS4368: Advanced Database
Slide # 1
PL/SQL
PL/SQL
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 2
PL/SQL
 Procedural Language for SQL (PL/SQL) is an extension of
Oracle SQL
 The basic intent of PL/SQL is
 increase the expressiveness of SQL
 process query results in a tuple-oriented way
 develop modular database application programs
 reuse program code, and
 reduce the cost for maintaining and changing applications.
 The basic construct of PL/SQL is a block
 constants and variables can be declared, and variables can be
used to store query results. Statements in a PL/SQL block include:





SQL statements
Control structures (loops)
Condition statements (if-then-else)
Exception handling
Calls of other PL/SQL blocks.
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 3
PL/SQL
 Each block builds a (named) program unit, and blocks can
be nested.
 The structure of a PL/SQL looks as follows:
(brackets [ ] enclose optional parts)
[<Block header>]
[declare
<Constants>
<Variables>
<Cursors>
<User defined exceptions>]
begin
<PL/SQL statements>
[exception
<Exception handling>]
end;
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 4
PL/SQL
 Consider the following simple code:
Needed to display output
Our local variable of data type DATE
Get today’s date and store it in our variable
Display the
contents of the
variable
Program Output
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 5
PL/SQL
 Numeric operations in PL/SQL:
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 6
PL/SQL
 Bind Variables:
 Host variables:




Declared in the SQL “Host Environment”
Remain active for the length of the SQL Session
Can be displayed with the SQL Print Command
Can only be accessed in the program when prefaced with a colon (:)
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 7
PL/SQL
 Interactive Input:
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 8
PL/SQL
 Control Structures: IF-THEN:
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 9
PL/SQL
 Control Structures: IF-THEN-ELSE:
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 10
PL/SQL
 Control Structures: IF-THEN-ELSIF:
Dr. Peeter Kirs
(Note Spelling)
Spring, 2003
CIS4368: Advanced Database
Slide # 11
PL/SQL
 Control Structures: Basic Loop:
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 12
PL/SQL
 Control Structures: While:
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 13
PL/SQL
 Control Structures: For:
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 14
PL/SQL
 SQL in PL:
 We must be careful about single record/field queries and
multiple return queries
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 15
PL/SQL
 Single Return Queries:
The data type applied to field
studentname is automatically
applied
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 16
PL/SQL
 Multiple Record Queries:
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 17
PL/SQL
 Remember our problem about calculating a student grade?
 Variable Declarations:
/* This program calculates a grade */
declare
cursor studentgrade is
select lastname, firstname, quiz1, quiz2, quiz3 from grades;
studentlastname grades.lastname%type;
studentfirstname grades.firstname%type;
q1
grades.quiz1%type;
q2
grades.quiz2%type;
q3
grades.quiz3%type;
average number;
sgrade
grades.grade%type;
nblanks number;
blanks
char(5);
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 18
PL/SQL
 Remember our problem about calculating a student grade?
begin
dbms_output.put_line('Student Name
Grade');
dbms_output.put_line('------------------ -----');
open studentgrade;
loop
fetch studentgrade into
studentlastname, studentfirstname, q1, q2, q3;
exit when studentgrade%notfound;
average := (q1 + q2 + q3)/3;
nblanks := 20 - (length(trim(studentfirstname))
+ length(trim(studentlastname)));
if average >= 90 then sgrade := 'A';
elsif average >= 80 then sgrade := 'B';
elsif average >= 70 then sgrade := 'C';
elsif average >= 60 then sgrade := 'D';
else sgrade := 'F';
end if;
dbms_output.put_line(trim(studentfirstname) || ' ' ||
trim(studentlastname) || lpad(' ',nblanks,' ') || sgrade);
update grades
set grade = sgrade;
end loop;
close studentgrade;
end;
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 19
PL/SQL
 Remember our problem about calculating a student grade?
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 20
PL/SQL
 Exceptions:
 Act as error handling routines
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 21
PL/SQL
 Types of Exceptions:
Exception Name
No_data_found
Too_Many_rows
Zero_Divide
Value_Error
Storage_Error
Login_Denied
Program_Error
Access_Into_Null
Description
Single row select returned no data
Single row select returned multiple rows
Attempt to divide by zero
Arithmetic, Conversion, Truncation error
PL/SQL ran out of memory or memory corrupted
Invalid Username or password
Run Time error
Attempt to assign values to uninitialized object
Invalid_Cursor
Rowtype_Mismatch
Illegal cursor operation
Cursor variable involved in incompatible return
types
--- And Others ---
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 22
PL/SQL
 Procedures:
Remember our Grading program?
 We could have created it as stored Procedure:
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 23
PL/SQL
 To run the program:
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 24
PL/SQL
 Functions, which are called by procedures, can also be
created and stored:
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 25
PL/SQL
 To call the function:
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 26
PL/SQL
 Triggers:
 A stored block which is implicitly called when an event occurs
 A triggering event is based on a Data Manipulation Language
statement such as:
• INSERT
• UPDATE
• DELETE
 Execution of the trigger is known as firing the trigger
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 27
PL/SQL
 Recall our problem about determining whether or not a
student had enrolled for two classes at the same time
 Information about students in a class was found only in the table
enrollment
 Information about when a class met was found only in the table
class
 If the information were in one table we could apply a
constraint which would not allow a student to enroll in both
classes:
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 28
PL/SQL
 However, even if we had created this table, it still would
not stop a student from enrolling in two classes that meet
at the same time
 Enrollment in a class is done by entering a record in table
enrollment (not table temp_table)
 One way to stop dual enrollment is to set a trigger which
tries to insert the record (from enrollment) into table
temp_table (which contains the constraint)
 If the record can be inserted into temp_table, it will then be inserted
into table enrollment
 If the record can NOT be inserted into temp_table, it will NOT be
inserted into table enrollment
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 29
PL/SQL
 The trigger might appear as:
 FOR EACH ROW is a row trigger which fires once for
each row inserted:
 :NEW refers to the new record to be inserted
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 30
PL/SQL
 Suppose we look up the Spring 2003 (semester = 102)
schedule for Yao Ming (studentid = 21098765):
 There is one other class that meets at the same time
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 31
PL/SQL
 If we now try and enroll Yao for the other class:
Dr. Peeter Kirs
Spring, 2003
CIS4368: Advanced Database
Slide # 32
PL/SQL
Dr. Peeter Kirs
Spring, 2003