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does this "top-200" query do a table scan
Posted by: Andrew Nuss
Date: October 27, 2015 05:50AM

I have a table "Article_t" with two particular columns:

"id_c" and progressMade_c", both of which are configured as "bigint"

id_c is the primarykey

progressMade_c is always initially zero, but when work begins on a row, it is updated to be the current timestamp in millis, until finally done, when it becomes the maximum positive value.

Aside from the primary key index, I have an index on (progressMade_c, id_c)

The basic idea is that I want an efficient query that not only fetches virgin (unworked on records) but also records whose "munging" failed to finish in a reasonable amount of time.

Does this query do a table scan, or if so, at least a very efficient one?

select id_c from Article_t where progressMade_c < :maxvalue limit 200

where :maxvalue is set to some parameter equal to the current timestamp minus 10 minutes?

Basically this is a "top-200" query of articles to work on, with the idea being that I want the minimum id values to be returned.

Andy

(InnoDB)

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