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

CIS4368: Advanced Database Slide # 1

PL/SQL

Dr. Peeter Kirs Spring, 2003

PL/SQL


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.

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.


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;


PL/SQL


Consider the following simple code:

Needed to display output

Our local variable of data type DATEGet today’s date and store it in our variable

Display the contents of the variableProgram Output


PL/SQL


Numeric operations in PL/SQL:


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 (:)


PL/SQL


Interactive Input:


PL/SQL


Control Structures: IF-THEN:


PL/SQL


Control Structures: IF-THEN-ELSE:


PL/SQL


Control Structures: IF-THEN-ELSIF: (Note Spelling)


PL/SQL


Control Structures: Basic Loop:


PL/SQL


Control Structures: While:


PL/SQL


Control Structures: For:


PL/SQL


SQL in PL:

We must be careful about single record/field queries and multiple return queries


PL/SQL


Single Return Queries:

The data type applied to field studentname is automatically applied


PL/SQL


Multiple Record Queries:


PL/SQL


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:


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;


PL/SQL


Remember our problem about calculating a student grade?


PL/SQL


Exceptions:

Act as error handling routines


PL/SQL


Types of Exceptions:

Exception NameNo_data_found

DescriptionSingle row select returned no data

Too_Many_rows Single row select returned multiple rows

Zero_Divide Attempt to divide by zeroValue_Error Arithmetic, Conversion, Truncation errorStorage_Error PL/SQL ran out of memory or memory corruptedLogin_Denied Invalid Username or passwordProgram_Error Run Time errorAccess_Into_Null Attempt to assign values to uninitialized object

Invalid_Cursor Illegal cursor operationRowtype_Mismatch Cursor variable involved in incompatible return

types

--- And Others ---


PL/SQL


Procedures: Remember our Grading program?

We could have created it as stored Procedure:


PL/SQL


To run the program:


PL/SQL


Functions, which are called by procedures, can also be created and stored:


PL/SQL


To call the function:


PL/SQL


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


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:


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


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


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


PL/SQL


If we now try and enroll Yao for the other class:


PL/SQL


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

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