PL/SQL can handle conversions between different families among the datatypes.
Conversion can be done in two ways.
Ø Explicit conversion
Ø Implicit conversion
EXPLICIT CONVERSION
This can be done using the built-in functions available.
IMPLICIT CONVERSION
PL/SQL will automatically convert between datatype families when possible.
Ex:
DECLARE
a varchar(10);
BEGIN
select deptno into a from dept where dname='ACCOUNTING';
END;
In the above variable a is char type and deptno is number type even though, oracle will automatically converts the numeric data into char type assigns to the variable.
PL/SQL can automatically convert between
Ø Characters and numbers
Ø Characters and dates
VARIABLE SCOPE AND VISIBILITY
The scope of a variable is the portion of the program in which the variable can be accessed. For PL/SQL variables, this is from the variable declaration until the end of the block. When a variable goes out of scope, the PL/SQL engine will free the memory used to store the variable.
The visibility of a variable is the portion of the program where the variable can be accessed without having to qualify the reference. The visibility is always within the scope. If it is out of scope, it is not visible.
Ex1:
DECLARE
a number; -- scope of a
BEGIN
--------
DECLARE
b number; -- scope of b
BEGIN
-----
END;
------
END;
Ex2:
DECLARE
a number;
b number;
BEGIN
-- a , b available here
DECLARE
b char(10);
BEGIN
-- a and char type b is available here
END;
-----
END;
Ex3:
<<my_block>>
DECLARE
a number;
b number;
BEGIN
-- a , b available here
DECLARE
b char(10);
BEGIN
-- a and char type b is available here
-- number type b is available using <<my_block>>.b
END;
------
END;
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