SQL / PL

PL / SQL
By,
C.Janani, AP / IT

Definition
• PL/SQL stands for Procedural Language extension of
SQL.
• Procedural features of programming languages.
• Developed by Oracle Corporation in the early 90’s to
enhance the capabilities of SQL.
• PL/SQL Block consists of three sections:
 The Declaration section (optional).
 The Execution section (mandatory).
 The Exception (or Error) Handling section (optional).
DECLARE
Variable declaration
BEGIN
Program Execution
EXCEPTION
Exception handling
END;

Advantages of PL/SQL
• Block Structures
• Procedural language Capability
• Better Performance
• Error Handling

Conditional Statements in PL/SQL
IF THEN ELSE STATEMENT
1) IF condition
THEN
statement 1;
ELSE
statement 2;
END IF;
2) IF condition 1
THEN
statement 1; statement 2;
ELSIF condtion2
THEN
statement 3;
ELSE
statement 4;
END IF
3) IF condition 1
THEN
statement 1;
statement 2;
ELSIF condtion2
THEN
statement 3;
ELSE statement 4;
END IF;
4) IF condition1
THEN
ELSE IF condition2 THEN statement1;
END IF;
ELSIF condition3
THEN
statement2;
END IF;

Iterative Statements in PL/SQL
• Simple Loop
• While Loop
• For Loop
LOOP statements; EXIT;
{or EXIT WHEN
condition;}
END LOOP;
WHILE <condition>
LOOP statements; END
LOOP;
FOR counter IN
val1..val2 LOOP
statements; END LOOP;

Cursors
• A temporary work area created in the system memory
when a SQL statement is executed.
• Contains information on a select statement and the
rows of data accessed by it.
• Can open a cursor, and repeatedly fetch a tuple then
move the cursor, until all tuples have been retrieved.
– Can use the ORDER BY clause, in queries that are accessed
through a cursor, to control the order in which tuples are
returned.
• Fields in ORDER BY clause must also appear in SELECT clause.
• Can also modify/delete tuple pointed to by a cursor.

Cursor Types:
• Implicit cursors
These are created by default when DML statements like,
INSERT, UPDATE, and DELETE statements are executed. They are
also created when a SELECT statement that returns just one row is
executed.
• Explicit cursors
They must be created when you are executing a SELECT
statement that returns more than one row. Even though the cursor
stores multiple records, only one record can be processed at a time,
which is called as current row. When you fetch a row the current
row position moves to next row.
• Both implicit and explicit cursors have the same functionality, but
they differ in the way they are accessed.

Stored Procedures
• A stored procedure or in simple a proc is a named PL/SQL block
which performs one or more specific task. This is similar to a
procedure in other programming languages.
• Has a header and a body.
• Header consists of the name of the procedure and the parameters
or variables passed to the procedure.
• The body consists or declaration section, execution section and
exception section similar to a general PL/SQL Block.
• A procedure is similar to an anonymous PL/SQL Block but it is
named for repeated usage.
• We can pass parameters to procedures in three ways.
1) IN-parameters
2) OUT-parameters
3) IN OUT-parameters
• A procedure may or may not return any value.

Syntax:
• CREATE [OR REPLACE] PROCEDURE proc_name
[list of parameters]
IS
Declaration section
BEGIN
Execution section
EXCEPTION
Exception section
END;

PL/SQL Functions
• The major difference between a procedure and a function is, a function must
always return a value, but a procedure may or may not return a value.
• General Syntax to create a function is
CREATE [OR REPLACE] FUNCTION function_name [parameters]
RETURN return_datatype;
IS
Declaration_section
BEGIN
Execution_section
Return return_variable;
EXCEPTION
exception section
Return
return_variable;
END;

Parameters in Procedure and Functions
1) IN type parameter: These types of parameters
are used to send values to stored procedures.
CREATE [OR REPLACE] PROCEDURE procedure_name ( param_name1 IN
datatype, param_name12 IN datatype ... )
2) OUT type parameter: These types of
parameters are used to get values from stored
procedures. This is similar to a return type in
functions.
CREATE [OR REPLACE] PROCEDURE proc2 (param_name OUT datatype)
3) IN OUT parameter: These types of parameters
are used to send values and get values from
stored procedures.
CREATE [OR REPLACE] PROCEDURE proc3 (param_name IN OUT datatype)

Exception Handling
• Using Exception Handling we can test the
code and avoid it from exiting abruptly.
• When an exception occurs a messages which
explains its cause is recieved.
• PL/SQL Exception message consists of three
parts.
1) Type of Exception
2) An Error Code
3) A message

Structure of Exception Handling
DECLARE
Declaration section
BEGIN
Exception section
EXCEPTION
WHEN ex_name1 THEN
-Error handling statements
WHEN ex_name2 THEN
WHEN Others THEN
END;

Types of Exception
a) Named System Exceptions
b) Unnamed System Exceptions
c) User-defined Exceptions
Named System Exceptions

Trigger
• Trigger is a pl/sql block structure which is fired
when a DML statements like Insert, Delete,
Update is executed on a database table.
• A trigger is triggered automatically when an
associated DML statement is executed.

Syntax of Triggers
CREATE [OR REPLACE ] TRIGGER trigger_name {BEFORE |
AFTER | INSTEAD OF }
{INSERT [OR] | UPDATE [OR] | DELETE}
[OF col_name]
ON table_name
[REFERENCING OLD AS o NEW AS n]
[FOR EACH ROW]
WHEN (condition)
BEGIN
--- sql statements
END;

Embedded SQL Example
#include<stdio.h>
#include<string.h>
EXEC SQL BEGIN DECLARE SECTION;
long station_id;
long mon;
float temp;
float rain;
char city_name[21];
long SQLCODE;
EXEC SQL END DECLARE SECTION;
main()
{
/* the CONNECT statement, if needed, goes here */
strcpy(city_name,"Denver");
EXEC SQL SELECT ID INTO :station_id
FROM STATION
WHERE CITY = :city_name;

if (SQLCODE == 100)
{
printf("There is no station for city %sn",city_name);
exit(0);
}
printf("For the city %s, Station ID is %ldn",city_name,station_id);
printf("And here is the weather data:n");
EXEC SQL DECLARE XYZ CURSOR FOR
SELECT MONTH, TEMP_F, RAIN_I FROM STATS
WHERE ID = :station_id
ORDER BY MONTH;
EXEC SQL OPEN XYZ;
while (SQLCODE != 100) {
EXEC SQL FETCH XYZ INTO :mon, :temp, :rain;
if (SQLCODE == 100)
printf("end of listn");
else
printf("month = %ld, temperature = %f, rainfall = %fn",mon,temp,rain);
}
EXEC SQL CLOSE XYZ;
exit(0);
}

• Execution log:
For the city Denver, Station ID is 44
And here is the weather data:
month = 1, temperature = 27.299999, rainfall = 0.180000
month = 7, temperature = 74.800003, rainfall = 2.110000
end of list

SQL / PL

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