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thevar1able/ClickHouse

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AggregateFunctions: implemented topK(n) This implements a new function for approximate computation of the most frequent entries using Filtered Space Saving with a merge step adapted from Parallel Space Saving paper. It works better for cases where GROUP BY x is impractical due to high cardinality of x, such as top IP addresses or top search queries.

2017-05-02 21:08:37 +00:00

SELECT topK(10)(n) FROM (SELECT if(number % 100 < 10, number % 10, number) AS n FROM system.numbers LIMIT 100000);