CUME_DIST ( expr [, expr]... ) WITHIN GROUP 
( ORDER BY 
  expr [ DESC | ASC ] [ NULLS { FIRST | LAST }] 
  [, expr [ DESC | ASC ] [ NULLS { FIRST | LAST }]]...
)

For information on the symbols and conventions of Backus-Naur Form (BNF) syntax, see Appendix A.