pi function
The pi function returns the value of pi, that is, 3.141592653589793. 
                  
Syntax:
double pi()Semantics:
                  - The pifunction does not expect any input arguments.
- return type: double.
Example:
                  SELECT pi() AS PI FROM ArcheryOutput:
                +-----------+-------------------+
 | PI        | 3.141592653589793 |
 +-----------+-------------------+