At 12:43 AM 8/30/2011, mysql-plain-digest-help@lists.mysql.com wrote:
>Not useful to add an index for that. I also wonder why the value is null
>(meaning: unknown, not certain) for almost all records.

It depends on if you want the forest or the trees. A frequently executed
query asks for just the robots. An index is an efficient way to select
6 of 20,000. As for why the rest are null, null is just a a random
everything else value, left over from before the "is_robot" column was
added.

Is there a better way to mark a small number of "special" records in a
big data set?


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