CIS4368: Advanced DatabaseSlide # 1 PL/SQL Dr. Peeter KirsSpring, 2003 PL/SQL

CIS4368: Advanced DatabaseSlide # 2 PL/SQL Dr. Peeter KirsSpring, 2003 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.  constants and variables can be declared, and variables can be used to store query results. Statements in a PL/SQL block include: The basic construct of PL/SQL is a block  SQL statements  Control structures (loops)  Condition statements (if-then-else)  Exception handling  Calls of other PL/SQL blocks.

CIS4368: Advanced DatabaseSlide # 3 PL/SQL Dr. Peeter KirsSpring, 2003 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) [ ] [declare ] begin [exception ] end;

CIS4368: Advanced DatabaseSlide # 4 PL/SQL Dr. Peeter KirsSpring, 2003 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

CIS4368: Advanced DatabaseSlide # 5 PL/SQL Dr. Peeter KirsSpring, 2003 Numeric operations in PL/SQL:

CIS4368: Advanced DatabaseSlide # 6 PL/SQL Dr. Peeter KirsSpring, 2003 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 (:)

CIS4368: Advanced DatabaseSlide # 7 PL/SQL Dr. Peeter KirsSpring, 2003 Interactive Input:

CIS4368: Advanced DatabaseSlide # 8 PL/SQL Dr. Peeter KirsSpring, 2003 Control Structures: IF-THEN:

CIS4368: Advanced DatabaseSlide # 9 PL/SQL Dr. Peeter KirsSpring, 2003 Control Structures: IF-THEN-ELSE:

CIS4368: Advanced DatabaseSlide # 10 PL/SQL Dr. Peeter KirsSpring, 2003 Control Structures: IF-THEN-ELSIF: (Note Spelling)

CIS4368: Advanced DatabaseSlide # 11 PL/SQL Dr. Peeter KirsSpring, 2003 Control Structures: Basic Loop:

CIS4368: Advanced DatabaseSlide # 12 PL/SQL Dr. Peeter KirsSpring, 2003 Control Structures: While:

CIS4368: Advanced DatabaseSlide # 13 PL/SQL Dr. Peeter KirsSpring, 2003 Control Structures: For:

CIS4368: Advanced DatabaseSlide # 14 PL/SQL Dr. Peeter KirsSpring, 2003 SQL in PL: We must be careful about single record/field queries and multiple return queries

CIS4368: Advanced DatabaseSlide # 15 PL/SQL Dr. Peeter KirsSpring, 2003 Single Return Queries: The data type applied to field studentname is automatically applied

CIS4368: Advanced DatabaseSlide # 16 PL/SQL Dr. Peeter KirsSpring, 2003 Multiple Record Queries:

CIS4368: Advanced DatabaseSlide # 17 PL/SQL Dr. Peeter KirsSpring, 2003 Remember our problem about calculating a student grade? /* 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);  Variable Declarations:

CIS4368: Advanced DatabaseSlide # 18 PL/SQL Dr. Peeter KirsSpring, 2003 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;

CIS4368: Advanced DatabaseSlide # 19 PL/SQL Dr. Peeter KirsSpring, 2003 Remember our problem about calculating a student grade?

CIS4368: Advanced DatabaseSlide # 20 PL/SQL Dr. Peeter KirsSpring, 2003 Exceptions: Act as error handling routines

CIS4368: Advanced DatabaseSlide # 21 PL/SQL Dr. Peeter KirsSpring, 2003 Types of Exceptions: Exception Name No_data_found Description Single row select returned no data Too_Many_rowsSingle row select returned multiple rows Zero_DivideAttempt to divide by zero Value_ErrorArithmetic, Conversion, Truncation error Storage_ErrorPL/SQL ran out of memory or memory corrupted Login_DeniedInvalid Username or password Program_ErrorRun Time error Access_Into_NullAttempt to assign values to uninitialized object Invalid_CursorIllegal cursor operation Rowtype_MismatchCursor variable involved in incompatible return types --- And Others ---

CIS4368: Advanced DatabaseSlide # 22 PL/SQL Dr. Peeter KirsSpring, 2003 Procedures: Remember our Grading program? We could have created it as stored Procedure:

CIS4368: Advanced DatabaseSlide # 23 PL/SQL Dr. Peeter KirsSpring, 2003 To run the program:

CIS4368: Advanced DatabaseSlide # 24 PL/SQL Dr. Peeter KirsSpring, 2003 Functions, which are called by procedures, can also be created and stored:

CIS4368: Advanced DatabaseSlide # 25 PL/SQL Dr. Peeter KirsSpring, 2003 To call the function:

CIS4368: Advanced DatabaseSlide # 26 PL/SQL Dr. Peeter KirsSpring, 2003 Triggers:  A stored block which is implicitly called when an event occurs INSERT  A triggering event is based on a Data Manipulation Language statement such as: UPDATE DELETE  Execution of the trigger is known as firing the trigger

CIS4368: Advanced DatabaseSlide # 27 PL/SQL Dr. Peeter KirsSpring, 2003 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:

CIS4368: Advanced DatabaseSlide # 28 PL/SQL Dr. Peeter KirsSpring, 2003 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

CIS4368: Advanced DatabaseSlide # 29 PL/SQL Dr. Peeter KirsSpring, 2003 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

CIS4368: Advanced DatabaseSlide # 30 PL/SQL Dr. Peeter KirsSpring, 2003 Suppose we look up the Spring 2003 (semester = 102) schedule for Yao Ming (studentid = ): There is one other class that meets at the same time

CIS4368: Advanced DatabaseSlide # 31 PL/SQL Dr. Peeter KirsSpring, 2003 If we now try and enroll Yao for the other class:

CIS4368: Advanced DatabaseSlide # 32 PL/SQL Dr. Peeter KirsSpring, 2003