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Editorial Team
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Asked: 2026-06-08T01:51:14+00:00

Im getting back into database design and i realize that I have huge gaps

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Im getting back into database design and i realize that I have huge gaps in my knowledge.

I have a table that contains categories. Each category can have many subcategories and each subcategory can belong to many super-categories.

I want to create a folder with a category name which will contain all the subcategories folders. (visual object like windows folders)
So i need to preform quick searches of the subcategories.

I wonder what are the benefits of using 1:M or M:N relationship in this case?
And how to implement each design?

I have create a ERD model which is a 1:M unary relationship. (the diagram also contains an expense table which stores all the expense values but is irrelevant in this case)

1:M unary relationship

is this design correct?

will many to many unary relationship allow for faster searches of super-categories and is the best design by default?

I would prefer an answer which contains an ERD

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1 Answer

  1. Editorial Team

    If I understand you correctly, a single sub-category can have at most one (direct) super-category, in which case you don’t need a separate table. Something like this should be enough:

    enter image description here

    Obviously, you’d need a recursive query to get the sub-categories from all levels, but it should be fairly efficient provided you put an index on PARENT_ID.

    Going in the opposite direction (and getting all ancestors) would also require a recursive query. Since this would entail searching on PK (which is automatically indexed), this should be reasonably efficient as well.

    For some more ideas and different performance tradeoffs, take a look at this slide-show.

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