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Editorial Team
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Asked: 2026-05-21T06:00:58+00:00

This was a pretty good question that was posed to me recently. Suppose we

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This was a pretty good question that was posed to me recently. Suppose we have a hypothetical (insert your favorite data storage tool here) database that consists of the names, ages and address of all the people residing on this planet. Your task is to print out the names of all the people whose age is greater than 18 within an HTML table. How would you go about doing that? Lets say that hypothetically the population is growing at the rate of 1200/per second and the database is updated accordingly(don’t ask how). What would be your strategy to print the names of all these people and their addresses on an HTML table?

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1 Answer

  1. Editorial Team

    1. Storing the ages in a DB tables sounds like a recipe for trouble to me – it would be impossible to maintain. You would be better off storing the birth dates, then building an index on that column/attribute.

    2. You have to get an initial dump of the table for display. Just calculate the date 18 years ago (let’s say D0) and use a query for any person born earlier than that.

    3. Use DB triggers to receive notifications about deaths, so that you can remove them from the table immediately.

    4. Since people only get older (unfortunately?), you can use ranged queries to get new additions (i.e. people that become 18 years old since yo last queried the table). E.g. if you want to update the display the next day, you issue a query for the people that were born in day D0 + 1 only – no need to request the whole table again.

    5. You could even prefetch the people who reach 18 years of age the next day, keep the entries in memory, and add them to the display at the exact moment they reach that age.

    BTW, even with 2KB of data for each person, you get a 18TB database (assuming 50% overhead). Any slightly beefed up server should be able to handle this kind of DB size. On the other hand, the thought of a 12 TB HTML table terrifies me…

    Oh, and beware of timezone and DST issues – time is such a relative thing these days…

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