We want to update dynamic dropdown

in this we want to update the dropdown on the basis of selection where if we select room type so the room no will reflect only on the basis of that.

we have three category of room type is standard,Royal,Executive and on that basis we have 101-standard,102-standard,201-royal,202-royal,301-executive,302-executive so please help on this.

You can use a filter on your second dropdown where the category is the category of the first selection (change to a single value column).