Oracle translates IN clause

[pando]

It always uses OR. Sometimes that OR can be implemented as an IN-list iterator in which an index is used for each element in the list.

You will notice that there is no index on SYS.DUAL but the IN() list is still converted to a set of OR conditions.

It doesnt always use OR if that´s the case then there wont be in-list iterator. Now if you say in-list iterator is implemented with OR then probably yes probably not, the point is it is not translated into several OR with in-list iterator. If I remember right inlist has something to do with some loopping mechanism in CBO better than concatating result sets

Regarding DUAL, since there is NO index then of course in-list iterator cannot be used so you see several ORs. If you read the quote I posted it says, a selective index must be present for in-list iterator to work