Is it okay to do binary search on an indexed column to get data from a non-indexed column? - mysql

Question

I have a large table users(id, inserttime, ...), with index only on id. I would like to find list of users who were inserted between a given start_date and finish_date range.
User.where(inserttime: start_date..finish_date).find_each
^This leads to a search which takes a lot of time, since the inserttime column is not indexed.
The solution which I came up with is to do find user.id for start_date and finish_date separately by doing a binary search twice on the table using the indexed id column.
Then do this to get all the users between start_id and finish_id:
User.where(id: start_id..finish_id).find_each
The binary search function I am using is something like this:
def find_user_id_by_date(date)
low = User.select(:id, :inserttime).first
high = User.select(:id, :inserttime).last
low_id = low.id
high_id = high.id
low_date = low.inserttime
high_date = high.inserttime
while(low_id <= high_id)
mid_id = low_id + ((high_id - low_id) / 2);
mid = User.select(:id, :inserttime).find_by(id: mid_id)
# sometimes there can be missing users. Ex: [1,2,8,9,10,16,17,..]
while mid.nil?
mid_id = mid_id + 1
mid = User.select(:id, :inserttime).find_by(id: mid_id)
end
if (mid.inserttime < date)
low_id = mid.id + 1
elsif (mid.inserttime > date)
high_id = mid.id - 1
else
return mid.id
end
end
# when date = start_date
return (low_id < high_id) ? low_id + 1 : high_id + 1
# when date = finish_date
return (low_id < high_id) ? low_id : high_id + 1
end
I am not sure if what I am doing is the right way to deal with this problem or even if my binary search function covers all the cases.
I think the best solution would be to add an index on inserttime column but that is sadly not possible.

Answer 1

This might not be the best way to do it, but if the IDs are numeric and sequential you could write a query to find the users in between the minimum and maximum user ID:
SELECT id
FROM users
WHERE id BETWEEN [low_id_here] AND [high_id_here];
In ActiveRecord:
low = User.select(:id, :inserttime).first
high = User.select(:id, :inserttime).last
low_id = low.id
high_id = high.id
User.where('id BETWEEN ? AND ?', low_id, high_id)