Disadvantages Of SQL:1. SQL does not have any procedural capabilities.2. SQL statements are passed to Oracle engine one at a time. Each time

the SQL statement is executed , the call is made to engine resources. This adds traffic on the network. Which decreases speed of data processing.

3. While processing SQL statement if an error occurs, the Oracle engine displays its own error message.

Programming in Oracle with PL/SQL

ProceduralLanguage Extension

toSQL

PL/SQL

• Allows using general programming tools with SQL, for example: loops, conditions, functions, etc.

• This allows a lot more freedom than general SQL.

• We write PL/SQL code in a regular file, for example PL.sql, and load it with @PL in the sqlplus console.

PL/SQL Blocks• PL/SQL code is built of Blocks, with a unique

structure.

• There are two types of blocks in PL/SQL:1. Anonymous Blocks: have no name (like scripts)

• can be written and executed immediately in SQLPLUS

• can be used in a trigger

2. Named Blocks:• Procedures

• Functions

Anonymous Block Structure:DECLARE (optional)

/* Here you declare the variables you will use in this block */

BEGIN (mandatory)/* Here you define the executable statements (what the

block DOES!)*/EXCEPTION (optional)

/* Here you define the actions that take place if an exception is thrown during the run of this block */

END; (mandatory)/

Always put a new line with only a / at the end of a block! (This tells Oracle to run the block)

A correct completion of a block will generate the following message :

PL/SQL procedure successfully completed

DECLARESyntax

Examples

identifier [CONSTANT] datatype [NOT NULL]

[:= | DEFAULT expr];

Declare birthday DATE; age NUMBER(2) NOT NULL := 27; name VARCHAR2(13) := 'Levi'; magic CONSTANT NUMBER := 77; valid BOOLEAN NOT NULL := TRUE;

Notice that PL/SQL includes all SQL types,

and more…

Declaring Variables with the %TYPE Attribute

Examples

DECLARE sname Sailors.sname%TYPE; fav_boat VARCHAR2(30); my_fav_boat fav_boat%TYPE := 'Pinta';...

Accessing column sname in table Sailors

Accessing another variable

Declaring Variables with the %ROWTYPE Attribute

Declare a variable with the type of a ROW of a table.

And how do we access the fields in reserves_record?

reserves_record Reserves%ROWTYPE;

reserves_record.sid:=9; Reserves_record.bid:=877;

Accessing table Reserves

• Control Structures:

• Conditional Control• Iterative Control• Sequential Control

1. Conditional Control:

if <condition> thensequence of statements;

end if;

IF-THEN-ELSIF Statements

. . .IF rating > 7 THEN v_message := 'You are great'; ELSIF rating >= 5 THEN v_message := 'Not bad';ELSE v_message := 'Pretty bad';END IF;. . .

• Write PL/SQL code that will except an account number from the user and debit amount of Rs. 2000 from a/c if the balance of a/c remains minimum Rs.500. The process is to be fired on Account table. account (ac_Id, Name, bal)

Declareac_bal number(10,2);ac_no varchar2(6);debit_amt number(5) :=2000;min_bal constant number(5,2):=500;

Beginac_no:=&ac_no;select bal into ac_balfrom accountwhere ac_id=ac_no;

ac_bal:=ac_bal - debit_amt;if ac_bal >= min_bal then update accounts set bal=bal – debit_amt where ac_Id=ac_no;end if;

End;

2. Iterative Control:i) Simple loopii) For loopiii) while loop

• i) Simple looploop sequence of statements;

end loop;• ii) For loop

for counter in [reverse]lowerbound .. Upperboundloop

sequence of statements; end loop;

• iii) while loopwhile <condition>loop <action>end loop;

• Write a PL/SQL block to calculate the area of a circle for a value of radius varying from 3 to 7. Store the radius & the corresponding values of calculated area in a table, ‘Areas’.

Declarepi constant number(4,2) := 3.14;radius number(5);area number(10,2);

Beginradius:=3;while radius<=7loop

area:=pi*power(radius,2);insert into areas values(radius,area);

end loop;End;

• Write a PL/SQL block of code for inverting a number 5639 to 9365.

Declaregiven_number(5):=‘5639’;str_len number(2);inverted_no varchar2(5);

Beginstr_len:=length(given_number);

for cntr in reverse 1 .. Str_lenloop inverted number := inverted_number||substr(given_number, cntr,1);

end loop;dbms_output.put_line(‘The given no. is’ || given_number)dbms_output.put_line(‘The inverted number is’ ||

inverted_number)End;

• Sequential Control:

goto <code block name>;

• Write PL/SQL block of code to achieve the following. If the price of product p1 is less than 4000, then change the price to 4000. Th price change is to be recorded in the old_price_table along with the product_no & the date on which the price was last changed.

Declareselling_price number(10,2)

Beginselect sell_price into selling_pricefrom product_masterwhere product_no=‘p1’;

if selling_price<4000 then goto add_old_price;else dbms_output.put_line(‘Current price’ || selling _price);end if<<Add_old_price>>update product_master set sell_price=4000 where product_no= ‘p1’insert into old_price (prduct_no, date_change, old_price)values(‘p1’, sysdate, selling_price);dbms_output.put_line(‘the new price of p1 is 4000’);

End;

• Error Handling in PL/SQL:

when <exception name> thenuser defined actions to be carried out;

• Types Of Exceptions:1. predefined exceptions:

They are raised automatically by the system during run time.

2. user defined Exceptions:They must be raised explicitly using Raise

statement.

• Some Predefined Exceptions:

1. No_data_found2. Cursor_already_open3. Dup_val_on_index4. Srorage_error5. Program_error6. Zero_divide7. Invalid_cursor8. Login_denied9. Invalid_cursor10. Too_many_rows

• User Defined Exception:exception name <exception>;

Raise Statement:raise <exception name>;

• Declareexception name <exception>;

Begin SQL sentense;

if condition thenraise <exception name>;

end if;Exception

when <exception name> thenuser defined actions to be carried out;

End;

• The X company wants to check qty_in_hand.if it is less than 500 the company wants to display msg.

Declarelo_val exception;qty item_master.qty_in_hand%type;

Beginselect qty_in_hand into qtyfrom item_master where itemcode=‘i100’;if qty<500 then raise lo_val;end if;

Exceptionwhen lo_val then dbms_output.put_line=(‘Qty not enogh’);

End;