[ RULES
  [ { UPDATE | UPSERT [ ALL ] } ]
  [ { AUTOMATIC | SEQUENTIAL } ORDER ]
  [ model_iterate_clause ]
]
( [ { UPDATE | UPSERT [ ALL ] } ]
cell_assignment [ order_by_clause ] = expr
  [,  [ { UPDATE | UPSERT [ ALL ] } ]
    cell_assignment [ order_by_clause ] = expr
  ]...
)