Re: Very specialised query

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Hi,

Le 26 mars 09 à 15:30, Matthew Wakeling a écrit :
Now, it happens that there is an algorithm for calculating overlaps which is really quick. It involves iterating through the table in order of the start variable and keeping a list of ranges which "haven't ended yet". When you read the next range from the table, you firstly purge all the ranges from the list that end before the beginning of the new range. Then, you output a result row for each element in the list combined with the new range, then you add the new range to the list.

This algorithm just doesn't seem to fit into SQL at all.

Maybe it's just that I didn't devote enough time to reading your detailed explanation above, but this part sounds like it could be done in an aggregate you'd use in a correlated subquery containing the right ORDER BY, couldn't it?
  http://www.postgresql.org/docs/8.3/interactive/sql-createaggregate.html

HTH,
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dim




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