L9 l10 server side programming

Database SystemsDatabase Systems
1
Server side DatabaseServer side Database
Programming using PL/SQLProgramming using PL/SQL
Version 1.1Version 1.1

What is PL/SQL?
 SQL
Structured language to access database
ANSI Standard
Declarative
○ Specifies what to access but not how to
- SELECT id, first_name, family_name FROM
authors
 PL/SQL
Developed by Oracle as a procedural extension to
SQL
Declare variables, IF..ELSE, WHILE & FOR loops,
functions, procedures and other features found in a
programming language
3

Server Side Programming
 PL/SQL executes inside DBMS
DBMS maintains Relational data
Also stores and executes Procedural code!
Advantages
Results from one query can be used as a
basis for the next query without having to
pull data from DBMS to client side for
processing!
4

Client Side Procedural logic
 DBMS maintains relational data
 Client side programs implement procedural
logic
Is there a problem?
 Performance impact due increased network
traffic
 Cumulative effect if many clients run at the same
time
 Code re-use may not be possible
 Many applications may incorporate processing that
are quite similar but sharing may not be easy!
5

PL/SQL - Basics
 Block structured
Basic program unit is a block
Contains variables, code and error handler
 A BLOCK is contained within BEGIN and END
statements with executable commands in
between
Must contain some commands, even if they do
nothing!
 PL/SQL programs must at least contain 1
block
 Blocks can be nested (block within another
block)
6

PL/SQL – Block Syntax
DECLARE
variable declarations
BEGIN
program code
EXCEPTION
exception handler code
END;
7
Optional

PL/SQL - EXCEPTIONs
 EXCEPTIONS
“unexpected errors” that occur during execution
occurs at run-time not at compile time!
 EXCEPTION HANDLER
Code that executes when EXCEPTION occurs
Makes the code more robust
 Oracle Server has many pre-defined errors
no_data_found, value_error, too_many_rows, others
8

PL/SQL - Anonymous Block
DECLARE
today date;
BEGIN
SELECT sysdate INTO today FROM dual;
DBMS_OUTPUT.PUT_LINE (‘Today -’ ||
today);
END;
• What exactly happens in this code?
• What is DUAL? (revision test !)
9

PL/SQL - Named Block
 Has a name and stored in Oracle Server
 Contains Header section
name,
key word - a function, procedure or trigger
type of value it returns in case of function
 At the time of creation, the code within
the named block is NOT executed but
compiled and stored in Oracle Server
10

PL/SQL - Data type - Character
DECLARE
family_name VARCHAR2 (20);
Age NUMBER(3);
 Assignment
family_name := ‘Anderson’;
Age := 21;
11

PL/SQL – %Type
 %TYPE
To map a variable directly to the same datatype as the
table column
DECLARE
author_id AUTHORS.ID%TYPE;
 PL/SQL variable ‘author_id’ is of same datatype
which is used to define column name ‘id’ of table AUTHORS.
 If column type changes PL/SQL Code would still work!
{Example: VARCHAR2(20) to VARCHAR(30)}
12

PL/SQL - Scope Rules
 Variables, procedures and functions can
be referenced by the code executing
inside the block in which they are
defined
 Understanding of scope of variables,
functions is especially important in the
context of nested blocks!
13

PL/SQL Scope Example
DECLARE
father_name VARCHAR2(20):='Patrick';
date_of_birth DATE:='20-Apr-1972';
BEGIN
DECLARE
child_name VARCHAR2(20):='Mike';
date_of_birth DATE:='12-Dec-2002';
BEGIN
DBMS_OUTPUT.PUT_LINE('Father''s Name: '||
father_name);
DBMS_OUTPUT.PUT_LINE('Date of Birth: '||
date_of_birth);
DBMS_OUTPUT.PUT_LINE('Child''s Name: '||
child_name);
END;
DBMS_OUTPUT.PUT_LINE('Date of Birth: '||
date_of_birth);
END;
/ 14

PL/SQL Operators
 Expressions consist of PL/SQL operators
and operands
Arithmetic Operators
○ **, *, /, +, -
Comparison Operators
○ =, <>, !=, <, >, <=, >=, LIKE, BETWEEN, IN, IS
NULL
Logical Operators
○ AND, OR, NOT
 String Operator – Concatenation using ‘||’
15

PL/SQL – NULL
 NULL means “UNKNOWN” value
 Use IS NULL or IS NOT NULL to check
for NULL value
 NULL value comparison with ‘= NULL’
or ‘!= NULL’ may produce
unpredictable results!
 Use NVL function when appropriate
NVL (<expression>, <value if expression is NULL>)
16

PL/SQL – SELECT sample
DECLARE
name VARCHAR2(20);
surname VARCHAR2(20);
BEGIN
SELECT first_name, family_name
INTO name, surname
FROM AUTHORS
WHERE id = 1 ;
DBMS_OUTPUT.PUT_LINE
(‘Row selected is : ‘ || name || ‘-’ || surname);
END;
17

Performing DML Operations from PL/SQL
(INSERT, UPDATE, and DELETE)
 You can write INSERT, UPDATE, and DELETE
statements directly in PL/SQL programs, without any
special notation:
 %ROWCOUNT Attribute: How Many Rows Affected So
Far?
 Example
SET SERVEROUTPUT ON;
BEGIN
UPDATE employees SET salary = salary * 1.05
WHERE ...;
dbms_output.put_line('Updated ' || SQL%ROWCOUNT || '
salaries.');
END;
/
18

PL/SQL – Program Flow Control
 Conditional execution
IF-THEN, IF-THEN-ELSE, IF-THEN-ELSIF
CASE
 Repeated execution until some condition
 LOOP-END LOOP, FOR-LOOP-END
LOOP
WHILE-LOOP-END LOOP
EXIT WHEN
 Jump to code section
GOTO
19

PL/SQL – Conditional Execution
IF <condition>
THEN
statement1;
statement2;
…..
END IF;
 can be evaluated to TRUE, FALSE or
NULL – statement1, statement2 etc., are
executed only if it evaluates to TRUE
20

IF Example
IF sales > quota THEN
compute_bonus(empid);
UPDATE payroll SET pay = pay + bonus
WHERE empno = emp_id;
END IF;
21

PL/SQL – IF-THEN-ELSE
IF <condition>
THEN
statement1;
statement2;
…..
ELSE
statement3;
statement4;
…..
END IF;
22

PL/SQL IF-THEN-ELSIF
IF <condition1>
THEN
statement1;
…..
ELSIF <condition2>
statement3;
……
ELSE
…..
END IF;
23

Example
BEGIN ...
IF sales > 50000 THEN bonus := 1500;
ELSIF sales > 35000 THEN bonus :=
500;
ELSE bonus := 100; END IF;
INSERT INTO payroll VALUES
(emp_id,
bonus, ...);
END;
24

PL/SQL – Simple Loop
 The EXIT-WHEN statement lets you complete a
loop if further processing is impossible or
undesirable.
 When the EXIT statement is encountered, the
condition in the WHEN clause is evaluated.
 If the condition is true, the loop completes and
control passes to the next statement.E.G.
LOOP
statement1;
……
EXIT {WHEN ….} ;
END LOOP;
26

PL/SQL LOOP Example
 In the following example, the loop
completes when the value of total
exceeds 25,000:
LOOP ...
total := total + salary;
EXIT WHEN total > 25000; -- exit loop if
condition is true
END LOOP;
27

PL/SQL – FOR LOOP
FOR counter IN number1..number2
LOOP
statement1;
……
END LOOP;
FOR counter IN REVERSE
number1..number2
28

PL/SQL – FOR LOOP Example
FOR i IN 1..3 LOOP -- assign the values 1,2,3 to
i
sequence_of_statements -- executes three
times
END LOOP;
29

PL/SQL – WHILE LOOP
WHILE <condition>
LOOP
statement1;
…..
END LOOP;
30

Pre-defined Errors - examples
 NO_DATA_FOUND
A SELECT INTO statement returns no rows, or your
program references a deleted element in a nested
table or an uninitialized element in an index-by table.
 TOO_MANY_ROWS
A SELECT INTO statement returns more than one
row.
 ZERO_DIVIDE
A program attempts to divide a number by zero.
31

PL/SQL Error Handling example
DECLARE
comm_missing EXCEPTION; -- declare own exception
name VARCHAR2(20);
surname VARCHAR2(20);
BEGIN
SELECT first_name, family_name INTO name, surname
FROM AUTHORS;
IF commission IS NULL THEN
RAISE comm_missing; -- raise exception
END IF;
bonus := (salary * 0.10) + (commission * 0.15);
EXCEPTION
WHEN comm_missing THEN
DBMS_OUPUT.PUT_LINE(‘Sorry cannot calculate bonus as there is no
commission’);
WHEN TOO_MANY_ROWS THEN
DBMS_OUPUT.PUT_LINE(‘To much information to store ‘);
END;
/
32

Subprograms
 An ideal way of writing Writing Reusable
PL/SQL Code
 PL/SQL has two types of subprograms
called procedures and functions, which can
take parameters and be invoked (called).
 a subprogram is like a miniature program,
beginning with a header followed by an
optional declarative part, an executable
part, and an optional exception-handling
part:
33

Procedure Example
PROCEDURE award_bonus (emp_id NUMBER) IS
bonus REAL;
comm_missing EXCEPTION;
BEGIN -- executable part starts here
SELECT comm * 0.15 INTO bonus FROM emp WHERE empno =
emp_id;
IF bonus IS NULL THEN
RAISE comm_missing;
ELSE
UPDATE payroll SET pay = pay + bonus
WHERE empno = emp_id;
END IF;
EXCEPTION -- exception-handling part starts here
WHEN comm_missing THEN ... END award_bonus;
.
.
.
34

Function Example
CREATE OR REPLACE FUNCTION square(
original NUMBER) RETURN NUMBER AS
original_squared NUMBER;
BEGIN
original_squared := original * original;
RETURN original_squared;
END;
/
35

Packages
 PL/SQL lets you bundle logically related types,
variables, cursors, and subprograms into a
package
 The packages defines a simple, clear,
interface to a set of related procedures and
types.
 Packages usually have two parts: a
specification and a body.
 The specification defines the application
programming interface; it declares the types,
constants, variables, exceptions, cursors, and
subprograms.
 The body fills in the SQL queries for cursors
and the code for subprograms.
36

Database Triggers
 A database trigger is a stored subprogram
associated with a database table, view, or event.
 The trigger can be called once, when some event
occurs, or many times, once for each row affected
by an INSERT, UPDATE, or DELETE statement.
 The trigger can be called after the event, to record
it or take some followup action. Or, the trigger can
be called before the event to prevent erroneous
operations or fix new data so that it conforms to
business rules.
38

Triggers Example
CREATE TRIGGER audit_sal
AFTER UPDATE OF sal ON emp
FOR EACH ROW
BEGIN
INSERT INTO emp_audit VALUES ...
END;
39

Cursors
 A cursor is a pointer to the private
memory area allocated by the Oracle
server.
 There are two types of cursors:
Implicit cursors: Created and managed
internally by the Oracle server to process
SQL statements
Explicit cursors: Explicitly declared by the
programmer
40

Processing Explicit Cursors
 The following three commands are used to
process an explicit cursor:
○ OPEN
○ FETCH
○ CLOSE
 Every explicit cursor has the following four
attributes:
○ cursor_name%FOUND
○ cursor_name%ISOPEN
○ cursor_name%NOTFOUND
○ cursor_name%ROWCOUNT
41

L9 l10 server side programming

More Related Content

What's hot (17)

Viewers also liked (20)

Similar to L9 l10 server side programming (20)

More from Rushdi Shams (20)

Recently uploaded (20)

L9 l10 server side programming

Editor's Notes