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Editorial Team
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Asked: 2026-06-11T09:15:01+00:00

I have data that looks roughly like this: user_id range start end 10 500

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I have data that looks roughly like this:

user_id   range   start   end
10        500     1       500
11        175
12        200

and need to transform it into something like this:

user_id   range   start   end
10        500     1       500
11        175     501     675
12        200     676     875

so each subsequent row’s start number is the previous row’s end number. the current row’s end number is the start number + range-1.

I was trying to do this purely in SQL but seem a bit stuck as this produces an error:

UPDATE  users U
SET     start = ( SELECT end+1 FROM users U2 WHERE U2.id = U.id - 1 )
WHERE   U.id > 1;

which results in You can't specify target table 'users' for update in FROM clause — and while I’m still playing around for a solution, seem unable to find one.

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1 Answer

  1. Editorial Team

    Look at this answer

    Basically, change your subquery portion with a subquery 

    (SELECT end+1 FROM (SELECT end, id FROM users) U2 WHERE U2.id = U.id - 1)

    It is dirty, but it should work. Be warn that it will be slow as hell if your tables are big (and depending on some other config values on your mysql server), and I do not recommend using this on production code.
    Also, you are asumming you have all subsequent user ids, wich may not be the case. If you have gaps on your ids, it will set null on the field or it may fail.

    If you have gaps on your IDs you could do something like this:

    (SELECT end+1 FROM (SELECT end, id FROM users) U2 WHERE U2.id < U.id LIMIT 1)
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