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Editorial Team
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Asked: 2026-05-22T14:58:58+00:00

This is from a homework question. We solved it by building the SQL query

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This is from a homework question. We solved it by building the SQL query dynamically. But we are interested if it is possible to do with pure SQL.

A simplification of what is desired:
There is a table with two columns: source id and destination id. Given an id and a number n, we need to find all id of distance smaller equal n from the given id.

Clarification Edit:
Think about the table as representing web-links. If the row (1,3) appears in the table, it means that web-page 1 has a link to web-page 3.
We need to find all webpages that are reachable from a starting web-page with n clicks or less.

Since it is a “curiosity” question, use whatever SQL implementation you prefer.
“Pure SQL” means everything that fits into the “structured query style”. Using loops is not considered “pure SQL” (for the sake of the question).

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1 Answer

  1. Editorial Team

    You cannot express transitive closure using relational algebra or pure old SQL, so a general solution for any N is not possible.

    The best you can do is choose the N at “compile time” and use lots of joins, as you already do in the dynamically generated query approach.

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