SGN Function Details
 
Syntax
  SGN(numeric-expression)
 
The SGN function returns a value depending on the sign of its
argument:
  - If numeric-expression > 0, then SGN(numeric-expression) returns 1.
  - If numeric-expression = 0, then SGN(numeric-expression) returns 0.
  - If numeric-expression < 0, then SGN(numeric-expression) returns -1.