how to create a variable in aql code example

Example 1: sql declare variable

-- Declare the variable to be used.
DECLARE @MyCounter int;

-- Initialize the variable.
SET @MyCounter = 0;

Example 2: local variables in sql

Local variables:
These variables can be used or exist 
only inside the function. These variables
are not used or referred by any other function.

Global variables:
These variables are the variables which
can be accessed throughout the program.
Global variables cannot be created
whenever that function is called.