Re: SELECT DISTINCT vs UNIQUE KEY
For more exact answers on this I suggest to ask in the "Optimizer" forum again.
I can just guess that SELECT DISTINCT orders the result set to eliminate duplicates. The result set and/or the sort files might not fit into memory (tmp_table_size, sort_buffer_size).
The INSERT SELECT algorithm does not require to store the whole result set. Every row can immediately be checked against the unique index.
It would be nice if the optimizer used this algorithm for SELECT DISTINCT implicitly, but seemingly it does not.
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July 18, 2006 04:39AM
Re: SELECT DISTINCT vs UNIQUE KEY
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July 19, 2006 02:06AM
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