Function that returns a unique id per session/connection similar to MySQL's CONNECTION_ID()

Design and implement a function that returns a unique id per session/connection similar to MySQL's CONNECTION_ID().

Implementation details
function session_id will be added. Function returns current session unique id represented as string. Parameter

 boolean isNiladic

will be added to UDF FunctionTemplate to indicate if a function is niladic (a function to be called without any parameters and parentheses)

Please note, this function will override columns that have the same name. Table alias should be used to retrieve column value from table.
Example:

select session_id from <table>  // returns the value of niladic function session_id 

select t1.session_id from <table> t1 // returns session_id column value from table