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47 lines
1.8 KiB
SQL
47 lines
1.8 KiB
SQL
SET group_by_two_level_threshold = 1, max_threads = 1;
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SELECT
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k,
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anyLast(s)
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FROM
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(
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SELECT
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123456789 AS k,
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'Hello 1234567890 1234567890 1234567890 1234567890 1234567890 1234567890' AS s
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UNION ALL
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SELECT
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234567890,
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'World 1234567890 1234567890 1234567890 1234567890 1234567890 1234567890'
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)
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GROUP BY k
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WITH TOTALS
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HAVING length(anyLast(s)) > 0
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ORDER BY k;
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/* There was a bug in implementation of WITH TOTALS.
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* When there was more than one block after aggregation,
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* nullptr is passed to IAggregateFunction::merge instead of pointer to valid Arena.
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*
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* To reproduce, we set 'group_by_two_level_threshold' to small value to enable two-level aggregation.
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* Only in two-level aggregation there are many blocks after GROUP BY.
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*
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* Also use UNION ALL in subquery to generate two blocks before GROUP BY.
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* Because two-level aggregation may be triggered only after a block is processed.
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*
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* Use large numbers as a key, because for 8, 16 bit numbers,
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* two-level aggregation is not possible as simple aggregation method is used.
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* These numbers are happy to hash to different buckets and we thus we have two blocks after GROUP BY.
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*
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* Also we use long strings (at least 64 bytes) in aggregation state,
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* because aggregate functions min/max/any/anyLast use Arena only for long enough strings.
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*
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* And we use function 'anyLast' for method IAggregateFunction::merge to be called for every new value.
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*
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* We use useless HAVING (that is always true), because in absense of HAVING,
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* TOTALS are calculated in a simple way in same pass during aggregation, not in TotalsHavingBlockInputStream,
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* and bug doesn't trigger.
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*
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* We use ORDER BY for result of the test to be deterministic.
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* max_threads = 1 for deterministic order of result in subquery and the value of 'anyLast'.
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*/
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