Introduction to PL/SQL

Introduction to PL/SQL Kristian Torp Department of Computer Science Aalborg University www.cs.aau.dk/˜torp

[email protected]

December 2, 2011

daisy.aau.dk Kristian Torp (Aalborg University)

Introduction to PL/SQL

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Outline

1

Introduction

2

Stored Procedures An Overview Data Types Parameter Parsing Cursors

3

Packages Case Study: Table API

4

Summary

Kristian Torp (Aalborg University)


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Outline

1

Introduction

2


3


4

Summary



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Learning Outcomes

Learning Outcomes Understand how code can be executed within a DBMS Be able to design stored procedures in general Be able to construct and execute stored procedures on Oracle Knowledge about the pros and cons of stored procedures

Note That Concepts are fairly DBMS independent All code examples are Oracle specific



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Prerequisites SQL Knowledge about the SQL select statement Knowledge about SQL modification statements, e.g., insert and delete Knowledge about transaction management, e.g., commit and rollback Knowledge about tables, views, and integrity constraints

Procedural Programming Language Knowledge about another programming language of the C family Knowledge about data types, e.g., int, long, string, and Boolean Knowledge of control structures, e.g., if, while, for, and case Knowledge of functions, procedures, parameters, and return values



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Motivation Purpose Move processing into the DBMS from client programs (database applications)

Advantages Code accessible to all applications I

Access from different programming languages

Very efficient for data intensive processing I

Process large data set, small result returned

Enhance the security of database applications I

Avoid SQL injection attacks

http://en.wikipedia.org/wiki/SQL_injection



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Motivation Purpose Move processing into the DBMS from client programs (database applications)

Advantages Code accessible to all applications I

Access from different programming languages

Very efficient for data intensive processing I

Process large data set, small result returned

Enhance the security of database applications I

Avoid SQL injection attacks

http://en.wikipedia.org/wiki/SQL_injection

Missing Standard Unfortunately, the major DBMS vendors each have their own SQL dialect Kristian Torp (Aalborg University)


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Overview Functionality SQL extended with control structures I

Control structures like if and loop statements

Used for I I I I

Stored procedures (and functions) Package (Oracle specific) Triggers Types a.k.a. classes (Oracle specific)

In very widely used in the industry I see http://www.tiobe.com/index.php/content/paperinfo/ tpci/index.html In the SQL standard called SQL/PSM I

PSM = Persistent Storage Model

Focus The focus is here on stored procedures and packages! Kristian Torp (Aalborg University)


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Outline

1

Introduction

2


3


4

Summary



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Motivation for Stored Procedures The Big Four Benefits Abstraction I

Increases readability

Implementation hiding I

Can change internals without effecting clients

Modular programs I

More manageable and easier to understand

Library I

Reuse, reuse, and reuse!

Note This is not different from any other procedural programming language!



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Outline

1

Introduction

2


3


4

Summary



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A Procedure: Hello, World! Example (The Start Program) c r e a t e o r r e p l a c e procedure h e l l o w o r l d i s begin dbms output . p u t l i n e ( ’ H e l l o , World ! ’ ) ; end ;

Note It is a procedure, i.e., not a function I

Both a procedure and a function is called a stored procedure

It is a begin and end language, not curly brackets: { and } It uses a built-in library dbms output.put line I I

The package dbms output has the procedure put line Uses the dot notation for invoking functions myPackage.myProcedure



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A Function: Calculating Your BMI Example (A BMI Function) c r e a t e o r r e p l a c e f u n c t i o n bmi ( h e i g h t i n t , w e i g h t f l o a t ) return f l o a t is begin i f h e i g h t 3 . 0 then dbms output . p u t l i n e ( ’ h e i g h t must be i n [ 0 . 3 , 3 . 0 ] meters ’ ) ; end i f ; i f w e i g h t 500 then dbms output . p u t l i n e ( ’No human ’ ’ s w e i g h t i s 500 kg ’ ) ; end i f ; r e t u r n weight / height ∗∗2; end ;

Note It takes two parameters height and weight It is a function, i.e., has a return statement It is strongly typed language, i.e., parameters and the return value Kristian Torp (Aalborg University)


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Executing Stored Procedures Example (Execute on Oracle server) −− t o enable o u t p u t from t h e s e r v e r SQL> s e t s e r v e r o u t p u t on



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Executing Stored Procedures Example (Execute on Oracle server) −− t o enable o u t p u t from t h e s e r v e r SQL> s e t s e r v e r o u t p u t on −− execute t h e procedure SQL> execute h e l l o w o r l d ;



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Executing Stored Procedures Example (Execute on Oracle server) −− t o enable o u t p u t from t h e s e r v e r SQL> s e t s e r v e r o u t p u t on −− execute t h e procedure SQL> execute h e l l o w o r l d ; −− execute t h e f u n c t i o n SQL>exec bmi ( 1 . 8 7 , 9 0 ) ; −− r e s u l t s i n an e r r o r , v a l u e r e t u r n e d by f u n c t i o n must be used !



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Executing Stored Procedures Example (Execute on Oracle server) −− t o enable o u t p u t from t h e s e r v e r SQL> s e t s e r v e r o u t p u t on −− execute t h e procedure SQL> execute h e l l o w o r l d ; −− execute t h e f u n c t i o n SQL>exec bmi ( 1 . 8 7 , 9 0 ) ; −− r e s u l t s i n an e r r o r , v a l u e r e t u r n e d by f u n c t i o n must be used ! −− Wrap t h e f u n c t i o n c a l l SQL>exec dbms output . p u t l i n e ( bmi ( 1 . 8 7 , 9 0 ) ) ;



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Executing Stored Procedures Example (Execute on Oracle server) −− t o enable o u t p u t from t h e s e r v e r SQL> s e t s e r v e r o u t p u t on −− execute t h e procedure SQL> execute h e l l o w o r l d ; −− execute t h e f u n c t i o n SQL>exec bmi ( 1 . 8 7 , 9 0 ) ; −− r e s u l t s i n an e r r o r , v a l u e r e t u r n e d by f u n c t i o n must be used ! −− Wrap t h e f u n c t i o n c a l l SQL>exec dbms output . p u t l i n e ( bmi ( 1 . 8 7 , 9 0 ) ) ;

Note Output from server is not enabled by default in a session! Return value of a function cannot be ignored!



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Using SQL in Stored Procedures Example (Use the Data Stored) c r e a t e o r r e p l a c e f u n c t i o n g e t s t a t u s ( s t u d e n t i d number ) r e t u r n varchar2 i s v s t a t u s varchar2 ( 5 0 ) ; begin s e l e c t s t a . dsc into v status from s t u d e n t stu , s t a t u s s t a where s t u . s t a t i d = s t a . s t a t i d and stu . sid = student id ; return v status ; end ;

Note The declaration of the variable v status The usage of the into keyword in the select statement The usage of the parameter student id in the select statement Kristian Torp (Aalborg University)


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Calling Other Procedures Example (Callee) c r e a t e o r r e p l a c e procedure p ( s t v a r c h a r 2 ) as begin dbms output . p u t l i n e ( s t ) ; end ;



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Example (Caller) c r e a t e o r r e p l a c e procedure c a l l p i s begin p ( ’ H e l l o ’ ) ; p ( ’ World ! ’ ) ; end ;



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Example (Caller) c r e a t e o r r e p l a c e procedure c a l l p i s begin p ( ’ H e l l o ’ ) ; p ( ’ World ! ’ ) ; end ;

Note Can call own and built-in stored procedures Will use the procedure p instead of dbms output.put line You are now officially a PL/SQL library builder!!! Kristian Torp (Aalborg University)


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Control Structures: A Crash Course I Example (The If Statement) c r e a t e o r r e p l a c e procedure pb ( v a l boolean ) i s begin i f v a l = t r u e then dbms output . p u t l i n e ( ’ t r u e ’ ) ; e l s i f v a l = f a l s e then dbms output . p u t l i n e ( ’ f a l s e ’ ) ; else dbms output . p u t l i n e ( ’ n u l l ’ ) ; end i f ; end ;

Note Is this stupid? Recall three-valued logic the root of all evil! We will use the procedure pb in the code that follows! Kristian Torp (Aalborg University)


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Control Structures: A Crash Course II Example (The While Statement) c r e a t e o r r e p l a c e procedure count 10 i s i i n t := 1; begin w h i l e i < 10 l o o p dbms output . p u t l i n e ( i ) ; i := i + 1; end l o o p ;

Note What is printed 1 to 9 or 1 to 10? PL/SQL also has a for statement, very different from C PL/SQL does not have increment/decrement operators, e.g., i −− or ++j PL/SQL does not have compound assignments, e.g., i +=7 or j ∗=2



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Surprises: In General Surprises The code is stored in the DBMS!

{ has been replaced by begin and } by end SQL and programming logic blends very nicely! I

A strong-point of PL/SQL

Procedures are different from functions The assignment operator is := and not = The comparison operator is = and not == Control structures are quite different from the C world Three-valued logic will time and again surprise you! Server output is not enabled by default I

Which is a big surprise



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Outline

1

Introduction

2


3


4

Summary



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An Example Example (Various Data Types)

c r e a t e o r r e p l a c e procedure u s e b a s i c t y p e s i s v s t r v a r c h a r 2 ( 3 0 ) : = ’A s t r i n g ’ ; v i n t i n t : = 2 ∗∗ 65; c p i c o n s t a n t f l o a t : = 3.14159265358979323846264338327950288419; v f l o a t f l o a t := v i n t ∗ c p i ; begin p( v str ); p( v int ); p( v float ); end ;

Output A string 36893488147419103232 115904311329233965478,149216911761758199

Note Forget what you think of data types and size! Very high precision on all number types in both SQL and PL/SQL The size of strings must be defined Kristian Torp (Aalborg University)


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Overview: Scalar Data Types Scalar Data Types Description Integers

Floats

Strings Boolean Date/time

Type

Examples

smallint int/integer positive number dec/decimal real varchar2 nvarchar2 char Boolean date timestamp

-100, 0, 100 -1000, 0, 1000 0, 1, 2, 3 10.3 123.456, 3.4 123456.7890 Hello, Theta-Join Tøger, Dæmon World, Noise True, False 2007-09-09 2009-09-09 12:34:56

Note Not all of these data types are available from within SQL! Kristian Torp (Aalborg University)


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Quiz: The Decimal Data Type Example (Rouding) create or v dec begin v dec dbms v dec dbms v dec dbms end ;

r e p l a c e procedure u s i n g d e c i m a l i s decimal ( 4 , 2 ) ; := 12.34; output . p u t l i n e ( v dec ) ; := 12.344; output . p u t l i n e ( v dec ) ; := 12.347; output . p u t l i n e ( v dec ) ;

Questions Will this compile, note that it is decimal(4,2)? What will be printed (if it compiles)? Are you surprised? Kristian Torp (Aalborg University)


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Overview: Other Data Types Special Data Types Description

Type

Composite

Large Objects Reference Types

Record Varray Table BLOB CLOB BFILE REF REF CURSOR

Note We will only use records in this lecture.



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Anchored Data Types: Type Example (Anchor for a Column) create or replace f u n c t i o n get status anchored ( s t u d e n t i d s t u d e n t . s i d%t y p e ) r e t u r n s t a t u s . dsc%t y p e i s v s t a t u s s t a t u s . dsc%t y p e ; begin s e l e c t s t a . dsc into v status from s t u d e n t stu , s t a t u s s t a where s t u . s t a t i d = s t a . s t a t i d and stu . sid = student id ; return v status ; end ;

Note The anchored type using the %type Very convenient of maintenance reasons (avoid “hard-wiring” types) I

Widely used, you are encouraged to use it!



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Anchored Data Types: Rowtype Example (Anchor for a Table) c r e a t e o r r e p l a c e procedure g e t c o u r s e r o w t y p e ( c o u r s e i d course . c i d%t y p e ) is v row course%rowtype ; v tmp v a r c h a r 2 ( 5 0 0 ) ; begin select ∗ into v row from course c where c . c i d = c o u r s e i d ; v tmp : = v row . cname | | ’ : ’ | | v row . dsc ; p ( v tmp ) ; end ;

Note The anchored type using the rowtype I

Creates a record

The dot notation for access elements of the record Kristian Torp (Aalborg University)


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Surprises: Data Type Note Strings are a basic type, not an object like in Java or C# I

A maximum size must be specified

The sizes of the basic data type are very different from C and Java Date and time are basic data types! I

This is very handy

The anchored types is something new compared to C and Java Booleans are not a basic data type in SQL but in PL/SQL I

This sometimes leads to very annoying problems

Support for composite data type is not very good in PL/SQL compared to C and Java LOB objects are plain stupid I

But sometimes necessary



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Outline

1

Introduction

2


3


4

Summary



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Overview Example create or v tmp begin v tmp −− v a l end ;

r e p l a c e procedure p i n ( v a l i n i n t ) i s int ; := val + 5; : = v a l + 5 ; / ∗ i l l e g a l v a l i s read − o n l y ∗ /

Example c r e a t e o r r e p l a c e procedure p i n o u t ( v a l i n o u t i n t ) i s begin val := val + 5; end ;

Example c r e a t e o r r e p l a c e procedure c a l l p s i s v in i n t := 10; v i n o u t i n t := 10; begin p in ( v in ) ; p( v in ) ; p in out ( v in out ) ; p( v in out ) ; end ;

When execute call ps prints 10 and 15, why? Kristian Torp (Aalborg University)


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Quiz Example c r e a t e o r r e p l a c e procedure p i n o u t ( v a l i n o u t i n t ) i s begin val := val + 5; end ;

Example c r e a t e o r r e p l a c e procedure c a l l p s i s v in i n t := 10; v i n o u t i n t := 10; begin p in ( v in ) ; p( v in ) ; p in out ( v in out ) ; p( v in out ) ; end ;

Questions What are the formal parameter(s)? What are the actual parameter(s)? Is it call-by-value or call-by-reference? Kristian Torp (Aalborg University)


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Out Parameters Example c r e a t e o r r e p l a c e procedure g e t x y c o o r ( c o o r i d i n i n t , x coor out i n t , y coor out i n t ) is begin x c o o r : = round ( c o o r i d / 4 . 2 ) ; −− s t u p i d c a l c u l a t i o n s y c o o r : = round ( c o o r i d / 7 . 5 ) ; end ;

Note in

and out parameters can both be used in same procedure

The out parameters are write-only More than one value is “returned” by the procedure The calculation is naturally plain stupid round

is the built-in rounding function



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Parameter Mode

Mode Mode

Description

in

Formal parameter is read-only Formal parameter is write-only Formal parameter is read-write

out in out

Note in

is the default parameter mode if the mode is not specified

Stored procedures cannot be overloaded on the parameter signature There is a nocopy compiler hint for in out parameters



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What is Wrong Here? c r e a t e procedure p r o c 1 ( i i n t ) is begin −− s n i p c o m p l i c a t e d s t u f f return i ; end ;

create function func 1 ( i i n t ) return i n t is begin −− s n i p c o m p l i c a t e d s t u f f return ’ hello ’ ; end ;

A

B

create function func 2 ( i i n t ) return i n t is begin −− s n i p c o m p l i c a t e d s t u f f return i ∗2; p ( ’ h e l l o world ’ ) ; end ;

create function func 3 ( i i n t ) return i n t is begin −− s n i p c o m p l i c a t e d s t u f f p ( ’ h e l l o world ’ ) ; end ;

C

D



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Avoid This



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Additional Comments on Parameters

Items to Notice A default value can be provided for each parameter Stored procedures cannot be overloaded on the parameter signature Stored procedures can be called by position or by name Works like in most programming languages, however different syntax!



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Outline

1

Introduction

2


3


4

Summary



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Overview

Definition A cursor is a mechanism that ensure a result set can be identified by a declarative language such as SQL and processed by a procedural language such as PL/SQL or C#



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Overview


Solution Solves the well-known impedance mismatch problem!



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Overview


Solution Solves the well-known impedance mismatch problem!

Generality Knowledge about cursors in PL/SQL is directly transferable to many other programming languages.



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The Unix ls command Example (List Tables) c r e a t e o r r e p l a c e procedure l s i s cursor c tables i s s e l e c t ∗ from c a t ; v t a b le n a m e c a t . table name%t y p e ; c a t . t a b l e t y p e%t y p e ; v type begin open c t a b l e s ; loop f e t c h c t a b l e s i n t o v table name , v t y p e ; e x i t when c t a b l e s%n o t f ou n d ; p ( v t a b le n a m e ) ; end l o o p ; close c tables ; end ;

Note The view tab is a table that contains all table names The cursor is declared, opened, fetched, and closed Kristian Torp (Aalborg University)


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Cursor Attributes

Attributes Attribute notfound found rowcount isopen

Type Boolean Boolean Integer Boolean

Description True if a record is fetched unsuccessfully True if a record is fetched successfully The number of records fetched from the cursor True if cursor is open

Note There are additional attributes for bulk operations.



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Quiz: Using rowcount Example c r e a t e o r r e p l a c e procedure l s c n t i s cursor c tables i s s e l e c t table name from c a t ; v t a b le n a m e c a t . table name%t y p e ; begin open c t a b l e s ; loop f e t c h c t a b l e s i n t o v t a b le n a m e ; e x i t when c t a b l e s%n o t f ou n d ; p ( c t a b l e s%rowcount | | ’ ’ | | v t a b le n a m e ) ; end l o o p ; close c tables ; end ;

Question What is printed? Kristian Torp (Aalborg University)


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Quiz: Using isopen? Example c r e a t e o r r e p l a c e procedure l s i s o p e n i s cursor c tables i s s e l e c t table name from c a t ; v t a b le n a m e c a t . table name%t y p e ; v s t a t u s boolean : = f a l s e ; begin v s t a t u s : = c t a b l e s%isopen ; pb ( v s t a t u s open c t a b l e s ; v s t a t u s : = c t a b l e s%isopen ; pb ( v s t a t u s loop f e t c h c t a b l e s i n t o v t a b le n a m e ; e x i t when c t a b l e s%n o t f ou n d ; end l o o p ; v s t a t u s : = c t a b l e s%isopen ; pb ( v s t a t u s close c tables ; v s t a t u s : = c t a b l e s%isopen ; pb ( v s t a t u s end ;

); );

); );

Question What is printed? Kristian Torp (Aalborg University)


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Outline

1

Introduction

2


3


4

Summary



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Introduction

Idea A class like concept Very good for building libraries I

A way to cluster related stored procedures

Has a header and a body (think C-style languages)



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Outline

1

Introduction

2


3


4

Summary



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Introduction Goal To build a uniform way to address the data stored in table!

Methods Name

Description

exist() to string() print()

Return true if primary key exists Return string representation of row Convenient way to display a row



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Introduction Goal To build a uniform way to address the data stored in table!

Methods Name

Description

exist() to string() print()

Return true if primary key exists Return string representation of row Convenient way to display a row

Note Many more methods can be envisioned Think object-relational mapping (ORM) tools



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Header File: Course Table Example (Header) c r e a t e o r r e p l a c e package ccourse i s f u n c t i o n e x i s t ( c i d course . c i d%t y p e ) r e t u r n boolean ; f u n c t i o n t o s t r i n g ( c i d course . c i d%t y p e ) r e t u r n s t r i n g ; procedure p r i n t ( c i d course . c i d%t y p e ) ; end ;

Note The header lists all the public stored procedures The naming convention table name course package name ccourse The design is influenced by the Object class from Java and C#



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Header File: Course Table Example (Header) c r e a t e o r r e p l a c e package ccourse i s f u n c t i o n e x i s t ( c i d course . c i d%t y p e ) r e t u r n boolean ; f u n c t i o n t o s t r i n g ( c i d course . c i d%t y p e ) r e t u r n s t r i n g ; procedure p r i n t ( c i d course . c i d%t y p e ) ; end ;

Note The header lists all the public stored procedures The naming convention table name course package name ccourse The design is influenced by the Object class from Java and C#

Quiz Why is the method called exist and not exists?



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Body File: Private Method and Cursor Example (Body) c r e a t e o r r e p l a c e package body ccourse i s −− p r i v a t e c o n s t a n t c e r r o r c i d n u l l c o n s t a n t i n t : = − 20001; −− a c u r s o r used i n t h e i m p l e m e n t a t i o n c u r s o r c u r e x i s t ( c v c i d course . c i d%t y p e ) i s s e l e c t c . c i d , c . cname , c . semester , c . dsc from course c where c . c i d = c v c i d ; −− a p r i v a t e method procedure c h e c k v a l i d c i d ( c i d course . c i d%t y p e ) i s begin i f c i d i s n u l l then raise application error ( c error cid null , ’ Course ID i s n u l l ’ ) ; end i f ; end ;



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Body File: Private Method and Cursor Example (Body) c r e a t e o r r e p l a c e package body ccourse i s −− p r i v a t e c o n s t a n t c e r r o r c i d n u l l c o n s t a n t i n t : = − 20001; −− a c u r s o r used i n t h e i m p l e m e n t a t i o n c u r s o r c u r e x i s t ( c v c i d course . c i d%t y p e ) i s s e l e c t c . c i d , c . cname , c . semester , c . dsc from course c where c . c i d = c v c i d ; −− a p r i v a t e method procedure c h e c k v a l i d c i d ( c i d course . c i d%t y p e ) i s begin i f c i d i s n u l l then raise application error ( c error cid null , ’ Course ID i s n u l l ’ ) ; end i f ; end ;

Note The method check valid cid is private Kristian Torp (Aalborg University)


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Body File: The Exist Method Example (Method) f u n c t i o n e x i s t ( c i d course . c i d%t y p e ) r e t u r n boolean i s r e c e x i s t c u r e x i s t%rowtype ; begin c h e c k v a l i d c i d ( c i d ) ; −− p r e c o n d i t i o n open c u r e x i s t ( c i d ) ; fetch cur exist into rec exist ; close c u r e x i s t ; r e t u r n ( r e c e x i s t . cid i s not n u l l ) ; end ;

Note Uses the private method check valid cid to check preconditions Uses the private cursor cur exist Returns true if a valid primary key is found



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Body File: The to string Method Example (Method) f u n c t i o n t o s t r i n g ( c i d course . c i d%t y p e ) r e t u r n s t r i n g i s v rv string (512); r e c e x i s t c u r e x i s t%rowtype ; begin c h e c k v a l i d c i d ( c i d ) ; −− p r e c o n d i t i o n open c u r e x i s t ( c i d ) ; fetch cur exist into rec exist ; close c u r e x i s t ; v r v : = ’ course name : ’ | | r e c e x i s t . cname | | ’ ’ | | ’ course desc : ’ | | r e c e x i s t . dsc ; return v rv ; end ;

Note Uses the private method check valid cid to check preconditions Uses the private cursor cur exist Kristian Torp (Aalborg University)


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Body File: The print Methods

Example (Method) procedure p r i n t ( c i d course . c i d%t y p e ) i s begin c h e c k v a l i d c i d ( c i d ) ; −− p r e c o n d i t i o n dbms output . p u t l i n e ( t o s t r i n g ( c i d ) ) ; end ;

Note Uses the private method check valid cid to check preconditions

print calls to string



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Exercising the Package Example SQL> s e t s e r v e r o u t p u t on −− execute t h e procedure SQL> execute ccourse . p r i n t ( 4 ) ;



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Note Similar to executing a stored procedure Access member by the dot notation



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Note Similar to executing a stored procedure Access member by the dot notation

Example SQL> execute ccourse . p r i n t ( n u l l ) ;

Note Results in an error “ORA-20001: Course ID is null”



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Summary: Packages Main Points Can have a public and a private part I

Has no protected access modifiers as in Java or C#

Is used to cluster related stored procedures Cursors, constants, and variables can be shared between methods in a package The foundation for building larger libraries in PL/SQL There is a huge library of built-it packages on Oracle Has very good exception handling facilities

Comparison to Object-Oriented Languages No inheritance Only static methods No concept of an object Kristian Torp (Aalborg University)


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Outline

1

Introduction

2


3


4

Summary



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Advantages

Advantages A complete programming language I

You are not missing stuff as you sometimes are in SQL

In wide-spread usage in the industry I

Adds to your market value

Very good integration of programming logic and SQL Impedance mismatch is basically removed I I

PL/SQL data types are super set of SQL data types Cursors enable the processing of sets (or bags)



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Disadvantages

Disadvantages Proprietary programming language There is a very large number (>1000) of reserved words I

Can be hard to come up with a variable name that is not a reserved word!

Pascal-family language (C-family more well-known) I

Which lead to a number of surprises

Object-oriented features are “clumsy” I

This has not been covered in this lecture



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Additional Information

Web Sites www.oracle.com/technology/tech/pl_sql/index.html PL/SQL’s home

www.psoug.org/library.html A very good and complete wiki with PL/SQL information

plsql-tutorial.com/ A crash course covering many PL/SQL features

en.wikibooks.org/wiki/Oracle_Programming/SQL_Cheatsheet A short overview of PL/SQL

www.java2s.com/Tutorial/Oracle/CatalogOracle.htm Many good examples, too many commercials



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Introduction to PL/SQL

Introduction to PL/SQL

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