>>>Doing a SELECT-distinct with a UNION or an INDEX Unique on APPENDed tables is simple enough....
>>>
>>>.... BUT ....
>>>
>>>The removed duplicates should be evenly distributed amongst the 4 origins! So that makes it a lot more complex...
>>>
>>>
>>What do you mean by removed duplicates distributed evenly among original?
>>
>>Do you mean that you should know in which table to keep the only correct record?
>>
>>E.g. say, you have
>>"Lennert Blom" in all 4 tables (and may be even repeatedly in some of them)
>>
>>In addition to creating the 5th table with only one correct set of records (no duplicates) you want to clean up the original tables to keep only unique records in them (e.g. leave only one Lennert Blom in one of the tables by some algorithm?)
>>
>>Did I get right your idea?
>
>If yes, you may have to calculate relative weight (or what's the right term? "удельный вес" in Russian) of each duplicate to the total number of records removed from each particular table...
>
>Anyway, let's see, if this is the exact problem you're trying to solve, because now I can see the complexity.

Why complexity? You calculate number of duplicates that needs to be deleted, then you calculate the deletion number for each of 4 tables, and then you scan and delete in each table counting delete total until you get the number. Obviously, during deletion you should reduce the total duplicate counter to keep the last record intact.