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Database SystemsDatabase Systems

Introduction to PL/SQL

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Procedural programming language Uses detailed instructions Processes statements sequentially

Combines SQL commands with procedural instructions

Used to perform sequential processing using an Oracle database

What is PL/SQL?

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PL/SQL Variables Variable names must follow the Oracle

naming standard Can use reserved words (BEGIN, NUMBER)

and table names for variable names, but is not a good practice

Make variable names descriptive Use lower-case letters, and separate

words with underscores Example: current_s_id

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Declaring PL/SQL Variables PL/SQL is a strongly-typed

language All variables must be declared prior to

use Syntax for declaring a variable:variable_name data_type_declaration;

Example:current_s_id NUMBER(6);

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PL/SQL Data Types Scalar

References a single value Composite

References a data structure Reference

References a specific database item LOB

References a large binary object

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Scalar Data Types Database scalar data types:

VARCHAR2 CHAR DATE LONG NUMBER

Non-database scalar data types: Integers: BINARY_INTEGER, INTEGER, INT,

SMALLINT Decimal numbers: DEC, DECIMAL, DOUBLE,

PRECISION, NUMERIC, REAL BOOLEAN

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Composite Data Types Reference multiple data elements,

such as a record Types:

RECORD TABLE VARRAY

Tabular structure that can expand or contract as needed

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Reference Data Types Reference a database item Assume data type of item

%TYPE: assumes data type of field %ROWTYPE: assumes data type of

entire row

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DECLAREVariable declarations

BEGINProgram statements

EXCEPTIONError-handling statements

END;

BodyBody

Variable Declarations

Variable Declarations

ExceptionSection

ExceptionSection

PL/SQL Program Structure

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May span multiple text editor lines

Each line ends with a semicolon

Text is not case sensitive

PL/SQL Program Lines

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Block of comments are delimited with /* */

/* <comment that spans more than one line of code> */

Single comment line starts with 2 hyphens-- comment on a single line

Comment Statements

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** Exponentiation 2 ** 3 8

* Multiplication 2 * 3 6

/ Division 9/2 4.5

+ Addition 3 + 2 5

- Subtraction 3 – 2 1

- Negation -5 Negative 5

Example ResultArithmetic Operators

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Assignment operator: := Variable being assigned to a new

value is on left side of assignment operator

New value is on right side of operator

student_name := ‘John Miller’;

student_name := current_student;

Assignment Statements

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Normally PL/SQL is used with other Oracle utilities such as forms or reports

You will learn to use PL/SQL in SQL*Plus Command to activate memory buffer in

SQL*Plus to enable output from PL/SQL programs:

SQL> SET SERVEROUTPUT ON SIZE buffer_size;

SQL> SET SERVEROUTPUT ON SIZE 4000;

Displaying PL/SQL Outputin SQL*Plus

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Command to output data from a PL/SQL program in SQL*Plus:

DBMS_OUTPUT.PUT_LINE(‘output string’);

DBMS_OUTPUT.PUT_LINE(‘Current Output:’);

Displaying PL/SQL ProgramOutput in SQL*Plus

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Copy program code from Notepad to SQL*Plus

Type / to execute

Executing a PL/SQL Programin SQL*Plus

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TO_DATE: character string to DATETO_DATE(‘07/14/01’, ‘MM/DD/YY’);

TO_NUMBER: character string to NUMBERTO_NUMBER(‘2’);

TO_CHAR: NUMBER or DATE to character string

TO_CHAR(2);

TO_CHAR(SYSDATE, ‘MM/DD/YYYY HH:MI’);

PL/SQL Data Type Conversion Functions

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Concatenating strings: joining 2 or more character strings into a single string

Concatenation operator: ||s_first_name := ‘Sarah’

s_last_name := ‘Miller’

s_full_name := s_first_name || ‘ ’ || s_last_name

Character String Functions

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RTRIM: removes blank trailing spacescust_address := RTRIM(cust_address);

LENGTH: returns string length (number of characters)

address_length := LENGTH(cust_address); UPPER, LOWER: changes characters to all

upper or lower cases_name := UPPER(s_name);s_name := LOWER(s_name);

PL/SQL Character String Functions

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INSTR: searches a string and looks for a matching substring and returns its starting positionstarting_position := INSTR(string_being_searched, search_string>);

blank_position := INSTR(‘Sarah Miller’, ‘ ’);

PL/SQL Character String Functions

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SUBSTR: extracts a specific number of characters from a string, starting at a given pointextracted_string := SUBSTR(string_being_searched, starting_point, number_of_characters_to_extract);

s_first_name := SUBSTR(‘Sarah Miller’, 1,5);

PL/SQL Character String Functions

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Syntax error Does not follow language guidelines Causes a PLS- compile error Examples: misspelling a reserved

word, using a function incorrectly Logic error

Program compiles correctly, but does not give correct output

Debugging PL/SQL Programs

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Isolate the line that is causing the error This may be before or after the line

that is flagged by the compiler Comment out lines as necessary

until program runs One error may cause several

cascading errors, so re-run program after fixing each error

Locating and Correcting Syntax Errors

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1. Identify the output variable(s) that have the error.

2. Identify the inputs and calculations that contribute to the error.

3. Display the values of the inputs using DBMS_OUTPUT commands.

4. Take a break and look at it again later.5. Ask a fellow student for help.6. Ask your instructor for help.

Locating and Fixing Logic Errors

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NULL Values in Assignment Statements Until a value is assigned to a

variable, the variable’s value is NULL Performing an arithmetic value on a

NULL value always results in a NULL value

Advice: Always initialize variable values

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IF/END IF:IF condition THEN

program statementsEND IF;

IF/ELSE/END IF:IF condition THEN

program statementsELSE

alternate program statements

END IF;

IF/THEN

PL/SQL Selection Structures

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IF/ELSIF:IF condition1 THEN

program statements;ELSIF condition2 THENalternate program statements;

ELSIF condition3 THENalternate program statements;

. . .ELSEalternate program statements;

END IF;

PL/SQL Selection Structures

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Operator Description Example

= Equal Count = 5

<>, != Not Equal Count <> 5

> Greater Than Count > 5

< Less Than Count < 5

>= Greater Than or Equal To

Count >= 5

<= Less Than or Equal To Count <= 5

PL/SQL Comparison Operators

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Evaluating NULL Conditions in IF/THEN Structures If a condition evaluates as NULL,

then it is FALSE How can a condition evaluate as

NULL? It uses a BOOLEAN variable that has

not been initialized It uses any other variable that has not

been initialized

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SQL Command Category

Purpose Examples Can be used in PL/SQL

Data Definition Language (DDL)

Change database structure

CREATE, ALTER, GRANT, REVOKE

No

Data Manipulation Language (DML)

View or change data

SELECT, INSERT, UPDATE, DELETE

Yes

Transaction Control

Create logical transactions

COMMIT, ROLLBACK

Yes

Using SQL Commands in PL/SQL Programs

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Loop: repeats one or more program statements multiple times until an exit condition is reached Pretest loop: exit condition is tested

before program statements are executed

Posttest loop: exit condition is tested after program statements are executed

PL/SQL Loops

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LOOP

program statements

IF condition THEN

EXIT;

END IF;

more program statements

END LOOP;

LOOP … EXIT

Pretest OR Posttest

Pretest OR Posttest

LOOP … EXIT Loop

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LOOPprogram statementsEXIT WHEN condition;

END LOOP;

Posttest Posttest

LOOP … EXIT WHEN Loop

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WHILE … LOOP

WHILE conditionLOOP

program statementsEND LOOP;

Pretest Pretest

WHILE Loop

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FOR counter_variable IN start_value .. end_valueLOOP program statementsEND LOOP;

Preset number of iterations

Preset number of iterations

Numeric FOR Loop

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Cursors Pointer to a server memory

location Contains information about a SQL

command in a PL/SQL program Called the command’s context area

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Cursor

contextarea

active setCID CALLID CNAME CCREDIT

1 MIS 101 Intro. to Info. Systems 32 MIS 301 Systems Analysis 33 MIS 441 Database Management 34 CS 155 Programming in C++ 35 MIS 451 Client/Server Systems 3

Number of rows

processed

Parsed commandstatement

Database Server Memory

Cursors

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Implicit Explicit

Types of Cursors

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Created automatically every time you use an INSERT, UPDATE, DELETE, or SELECT command

Doesn’t need to be declared Can be used to assign the output of a

SELECT command to one or more PL/SQL variables

Can only be used if query returns one and only one record

Implicit Cursors

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SELECT field1, field2, …

INTO variable1, variable2, …

FROM tablename

WHERE search_condition_that_will_

return_a_single_record;

Implicit Cursor Syntax

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Must be declared in program DECLARE section

Can be used to assign the output of a SELECT command to one or more PL/SQL variables

Can be used if query returns multiple records or no records

Explicit Cursors

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Declare the cursor Open the cursor Fetch the cursor result into

PL/SQL program variables Close the cursor

Using an Explicit Cursor

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Declaring an Explicit Cursor

DECLARE

CURSOR cursor_name IS SELECT_statement;

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Opening an Explicit Cursor

OPEN cursor_name;

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Fetching Explicit Cursor Records

FETCH cursor_name INTO variable_name(s);

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Closing an Explicit Cursor

CLOSE cursor_name;

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Processing an Explicit Cursor LOOP ..EXIT WHEN approach:OPEN cursor_name;

LOOP

FETCH cursor_name INTO variable_name(s);

EXIT WHEN cursor_name%NOTFOUND:

END LOOP;

CLOSE cursor_name;

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Processing an Explicit Cursor Cursor FOR Loop approach:

FOR variable_name(s) in cursor_name LOOP

additional processing statements;

END LOOP;

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Using Reference Data Types in Explicit Cursor Processing

Declaring a ROWTYPE reference variable:

DECLARE

reference_variable_name cursor_name%ROWTYPE;

Referencing a ROWTYPE reference variable:

reference_variable_name.database_field_name

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Attribute Return Value

%NOTFOUND TRUE when no rows left to fetch; FALSE when rows left to fetch

%FOUND TRUE when rows left to fetch; FALSE when no rows left to fetch

%ROWCOUNT Number of rows a cursor has fetched so far

%ISOPEN TRUE if cursor is open and FALSE is cursor is closed

Explicit Cursor Attributes

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Data structure that contains multiple data items that are the same data type

Each table item has a key and a value

Key values do not need to be sequential

Used to create a lookup table that is stored in memory to improve processing speed

PL/SQL TablesKey Value

1 Shadow

2 Dusty

3 Sassy

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PL/SQL Table of Records PL/SQL table that can store

multiple values that are referenced by a key

Usually used to store database records that need to be processed by a PL/SQL program

Improves performance by limiting number of database retrievals

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PL/SQL Exception Handling All error handling statements are

placed in the EXCEPTION program block

Exception handler: program command that provides information about an error, and suggest correction actions

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Common errors that have been given predefined names that appear instead of error numbers

Error Code Exception Name Description ORA-00001 DUP_VAL_ON_INDEX Unique constraint violated ORA-01001 INVALID_CURSOR Illegal cursor operation

ORA-01403 NO_DATA_FOUND Query returns no records

ORA-01422 TOO_MANY_ROWS Query returns more rows than expected

ORA-01476 ZERO_DIVIDE Division by zero ORA-01722 INVALID_NUMBER Invalid numeric conversion

ORA-06502 VALUE_ERROR Error in arithmetic or numeric function operation

Predefined Exceptions

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Exception Handler SyntaxFor Predefined Exceptions

WHEN exception1_name THEN

exception handling statements;

WHEN exception2_name THEN

exception handling statements;

…

WHEN OTHERS THEN

exception handling statements;

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Less-common errors that have not been given predefined names

ORA- error code appears Exception handler tests for ORA-

error code and provides alternate error message

Undefined Exceptions

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Errors that will not cause a run-time error, but will violate business rules

Programmer creates a custom error message

User-Defined Exceptions

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Nested PL/SQL Program Blocks An inner

program block can be nested within an outer program block

DECLARE variable declarationsBEGIN program statements

EXCEPTION error handling statementsEND;

DECLARE variable declarationsBEGIN program statementsEXCEPTION error handling statementsEND;

Inner block

Outer block

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Exception Handling in Nest Program Blocks If an exception is raised and

handled in an inner block, program execution resumes in the outer block

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DECLARE variable declarationsBEGIN program statements

additional program statementsEXCEPTION error handling statementsEND;

Exception Handling in Nested Program Blocks

DECLARE exception_ABEGIN RAISE exception_AEXCEPTION exception_A error handlerEND;

Exception is raised andhandled in inner block

Program executionresumes here

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Exception Handling in Nested Program Blocks Exceptions raised in inner blocks

can be handled by exception handlers in outer blocks