RULES
  [ { UPDATE | UPSERT [ ALL ] } ]
  [ { AUTOMATIC | SEQUENTIAL } ORDER ]
   [ ITERATE (number) [ UNTIL (condition) ] ]
( [ { UPDATE | UPSERT [ ALL ] } ]
cell_assignment [ order_by_clause ] = expr
  [ [ { UPDATE | UPSERT [ ALL ] } ]
    cell_assignment [ order_by_clause ] = expr
  ]...
)