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Asked: 2026-06-02T23:36:10+00:00

This is a problem of space vs time, I guess. Consider a online quizzing

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This is a problem of space vs time, I guess.

Consider a online quizzing application. In the browse-quizzes, with every quiz, I wish to show how many questions it has.

  • If a quiz has 10 questions, I may show it as “10 questions”, or “medium duration quiz”.
  • If a quiz has 5 questions, I may show it as “5 questions”, or “short duration quiz”.

In the Quiz table, I don’t have a column for storing the number of questions.
To find that number of questions, I can do 

SELECT COUNT(question_id) 
FROM Quiz 
NATURAL JOIN Quiz_data 
WHERE quiz_id = '$quiz_id'

Note that Quiz_data is a cross table of Quiz and Question_bank (i.e. it stores PKs of both the 2 table).

Note that if I store the *number_of_question* in Quiz, questions may be added/subtracted from Quiz. So apart from delete and insert, one needs to update as well.

Question: should I compute each time, or store the value in the Quiz table? The post title says the same question in general sense.

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1 Answer

  1. Editorial Team

    You need to know

    (1) how often your data changes, and
    (2) how much effort it takes to determine that number.

    As a general recommendation, I would look at:

    • If the data changes only very rarely -> you should calculate and then store that value.

    • If the cost of determining that number is very high -> try to calculate once, store and reuse.

    • On the other hand, if having an accurate count is crucial -> determine it as needed.

    This is not a clear-cut yes-or-no decision – it really depends on your data, your requirements, and how costly it is to calculate such a number/count.

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