Basic Plsql

8/2/2019 Basic Plsql

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Introduction to PL/SQL


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Fundamentals of PL/SQL

Full-featured programming language

An interpreted language Type in editor, execute in SQL*Plus


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Variables and Data Types

VariablesUsed to store numbers, character

strings, dates, and other data values

Avoid using keywords, table names andcolumn names as variable names

Must be declared with data type beforeuse: variable_namedata_type_declaration;


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Scalar Data Types

Represent a single value


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Composite and Reference Variables

Composite variablesRECORD: contains multiple scalar values, similar to a table

record

TABLE: tabular structure with multiple columns and rowsVARRAY: variable-sized array

Reference variablesDirectly reference a specific database field or record and assume

the data type of the associated field or record%TYPE: same data type as a database field%ROWTYPE: same data type as a database record


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PL/SQL Program Blocks


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Arithmetic Operators


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Assignment Statements

Assigns a value to a variable

variable_name := value; Value can be a literal:

current_s_first_name := 'John';

Value can be another variable:current_s_first_name := s_first_name;


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Executing a PL/SQL


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PL/SQL Data Conversion

Functions


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Manipulating Character

Strings To concatenate two strings in PL/SQL, you use the

double bar (||) operator:new_string := string1 || string2;

To remove blank leading spaces use the LTRIM function:string := LTRIM(string_variable_name);

To remove blank trailing spaces use the RTRIM function:string := RTRIM(string_variable_name);

To find the number of characters in a character string

use the LENGTH function:string_length := LENGTH(string_variable_name);


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Manipulating Character

Strings To change case, use UPPER, LOWER, INITCAP

INSTR function searches a string for a specific

substring:start_position := INSTR(original_string, substring);

SUBSTR function extracts a specific number ofcharacters from a character string, starting at a

given point:extracted_string := SUBSTR(string_variable,

starting_point, number_of_characters);


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PL/SQL Decision Control

Structures Use IF/THEN structure to execute code if condition is true

IF condition THENcommands that execute if condition is TRUE;

END IF;

If condition evaluates to NULL it is considered false Use IF/THEN/ELSE to execute code if condition is true or false

IF condition THENcommands that execute if condition is TRUE;

ELSE

commands that execute if condition isF

ALSE

;END IF;

Can be nested be sure to end nested statements


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PL/SQL Decision Control

Structures Use IF/ELSIF to evaluate many conditions:

IF condition1 THEN

commands that execute if condition1 is TRUE;

ELSIF condition2 THENcommands that execute if condition2 is TRUE;

ELSIF condition3 THENcommands that execute if condition3 is TRUE;

...ELSE

commands that execute if none of theconditions are TRUE;

END IF;


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Complex Conditions

Created with logical operators AND, ORand NOT

AND is evaluated before OR

Use () to set precedence


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Loops

Program structure that executes a series ofprogram statements, and periodically evaluatesan exit condition to determine if the loop shouldrepeat or exit

Pretest loop: evaluates the exit condition beforeany program commands execute

Posttest loop: executes one or more program

commands before the loop evaluates the exitcondition for the first time PL/SQL has 5 loop structures


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The LOOP...EXIT Loop

LOOP

[program statements]

IF condition THEN

EXIT;

END I

F;

[additional program statements]

END LOOP


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The LOOP...EXIT WHEN Loop

LOOP

program statementsEXIT WHEN condition;

END LOOP;


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The WHILE...LOOP

WHILE condition LOOP

program statementsEND LOOP;


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The Numeric FOR Loop

FOR counter_variable IN start_value

.. end_valueLOOP

program statements

END LOOP;


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Cursors

Pointer to a memory location that

the DBMS uses to process a SQLquery

Use to retrieve and manipulatedatabase data


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ImplicitCursor

Executing a SELECT query creates an implicitcursor

To retrieve it into a variable use IN

TO

: SELECT field1, field2, ...INTO variable1, variable2, ...FROM table1, table2, ...WHERE join_ conditions

AND search_condition_to_retrieve_1_record; Can only be used with queries that return

exactly one record


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ExplicitCursor

Use for queries that return

multiple records or no records

Must be explicitly declared andused


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Using an ExplicitCursor Declare the cursor

CURSOR cursor_name IS select_query;

Open the cursor

OPEN cursor_name; Fetch the data rows

LOOP

FETCH cursor_name INTO variable_name(s);

EXIT WHEN cursor_name%NOTFOUND; Close the cursor

CLOSE cursor_name;


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Cursor FOR Loop

Automatically opens the cursor, fetchesthe records, then closes the cursor

FOR variable_name(s) IN cursor_nameLOOP

processing commands

END LOOP; Cursor variables cannot be used outside

loop


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Handling Runtime Errorsin PL/SQL Programs

Runtime errors cause exceptions Exception handlers exist to deal with different

error situations Exceptions cause program control to fall to

exception section where exception is handled


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Predefined Exceptions


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Undefined Exceptions

Less common errors Do not have predefined names

Must declare your own name for theexception code in the declaration sectionDECLARE

e_exception_name EXCEPTION;

PRAGMAEXCEPTION_INIT(e_exception_name,

-Oracle_error_code);


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User-Defined Exceptions

Not a real Oracle error Use to enforce business rules


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Summary

PL/SQL is a programming language for workingwith an Oracle database

Scalar, composite and reference variables can beused

The IF/THEN/ELSE decision control structureallows branching logic Five loop constructs allow repeating code Cursors are returned from queries and can be

explicitly iterated over Exception handling is performed in the exceptionsection. User defined exceptions help to enforcebusiness logic


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Overview of PL/SQLStored Program Units

Self-contained group of programstatements that can be used within a

larger program. Easier to conceptualize, design, and debug Save valuable programming time because

you can reuse them in multiple database

applications Other PL/SQL programs can reference

them


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Overview of PL/SQLStored Program Units

Server-side program units stored inthe database as database objects andexecute on the database server

Client-side program units stored in

the file system of the clientworkstation and execute on the clientworkstation


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Types of Program Units


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Creating Stored Program Units

Procedure: a program unit that canreceive multiple input parameters andreturn multiple output values or return nooutput values

Function: a program unit that canreceive multiple input parameters, andalways returns a single output value.


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Parameter Declarations List

Defines the parameters and declarestheir associated data types

Enclosed in parentheses

Separated by commas


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Parameter Declarations List

Parameter mode describes how the programunit can change the parameter value:

IN

- specifies a parameter that is passed to theprogram unit as a read-only value that the programunit cannot change.

OUT - specifies a parameter that is a write-only valuethat can appear only on the left side of an assignment

statement in the program unitINOUT - specifies a parameter that is passed to the

program unit, and whose value can also be changedwithin the program unit


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Calling a Stored Procedure

From SQL*Plus command line:

EXEC

UTE

procedure_name(parameter1_value, parameter2_value,...);

From PL/SQL program:

Omit execute command


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Calling a Function

variable_name :=function_name(parameter1, parameter2,

...); Select function_name(parameter1,

parameter2, ...)

from dual;


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Packages

Another way to make PL/SQL programunits available to multiple applications

A code library that contains relatedprogram units and variables

Stored in the database and executes on

the database server


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Package Specification

Also called package header Declares package objects, including

variables, cursors, procedures, andfunctions, Use to declare public variables:

Remain in memory after the programs that

declare and reference them terminateDeclared in the DECLARE section of a packageReferenced same as private variables


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Package Specification


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Package Header

Package_name identifies the package

Must adhere to the Oracle Naming Standard

Declare the package objects in any order

Package can consist of just variabledeclarations, or it can consist of just

procedure or function declarations


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Procedure and FunctionDeclarations

Declare a procedure:PROCEDURE procedure_name

(parameter1 parameter1_data_type,parameter2 parameter2_data_type, ...);

Declare a function:FUNCTION function_name

(parameter1 parameter1_data_type,parameter2 parameter2_data_type, ...)

RETURN return_datatype;


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Package Body

Contains the implementation ofdeclared procedures and functions

Specification comes before body

Optional: sometimes a packagecontains only variable or cursor

declarations, and no procedure orfunction declarations


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Package Body

Package_name in the package body must be the sameas package_name in the package specification

Variables that you declare at the beginning of the

package body are private to the package Each package program unit has its own declaration

section and BEGIN and END statements

Each program unit declared in the package body must

have a matching program unit forward declaration in thepackage specification, with an identical parameter list


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Creating a Package Header


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Creating a Package Body


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Using Package Objects

Must preface the item with thepackage name:

package_name.item_name.

To grant other users the privilege toexecute a package:

GRANT EXECUTEON package_name TO

username;


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Database Triggers

Program units that execute in response tothe database events of inserting,updating, or deleting a record

Different from form triggers Useful for maintaining integrity constraints

and audit information

Cannot accept input parameters

Executes only when its triggering eventoccurs


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Trigger Properties

Trigger timing:

Defines whether a trigger fires before orafter the SQL statement executes

Can have the values BEFORE or AFTER

Trigger statement:

Defines the type of SQL statement thatcauses a trigger to fire

Can be INSERT, UPDATE, or DELETE


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Trigger Properties

Trigger level:Defines whether a trigger fires once for each

triggering statement or once for each row affected bythe triggering statement

Can have the values

ROWor STAT

EMEN

TStatement-level triggers fire once, either before or

after the SQL triggering statement executes.

Row-level triggers fire once for each row affected bythe triggering statement

Use :OLD.fieldname to reference previous value

Use :NEW.fieldname to reference changed value


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Creating Database Triggers


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Database Trigger Header

Trigger_name must follow Oracle NamingStandard

Join statement types using the OR

operator to fire for multiple statementtypes (INSERT OR UPDATE)

WHEN (condition) clause:

Trigger will fire only for rows that satisfy aspecific search condition

WHENOLD.grade IS NOT NULL;


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Database Trigger Body

Contains the commands that executewhen the trigger fires

PL/SQL code block that contains the usual

declaration, body, and exception sections Cannot contain transaction control

statements

Reference the

NEWand

OLD field valuesonly in a row-level trigger

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