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By default uniqCombined() uses 32-bit hash for all types except String, so this means that you cannot use uniqCombined() with i.e UInt64 and cardinality > UINT_MAX, although you can use uniqCombined(toString()) and this will lead to 64-bit hash, but will not have good performance. So uniqCombined64() had been introduced to fix this. Requires: #7213
10 lines
418 B
SQL
10 lines
418 B
SQL
-- for small cardinality the 64 bit hash perform worse, but for 1e10:
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-- 4 byte hash: 2.8832809652e10
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-- 8 byte hash: 0.9998568925e10
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-- but hence checking with 1e10 values takes too much time (~45 secs), this
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-- test is just to ensure that the result is different (and to document the
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-- outcome).
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SELECT uniqCombined(number) FROM numbers(toUInt64(1e7));
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SELECT uniqCombined64(number) FROM numbers(toUInt64(1e7));
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