Sql recursive query that gets all ancestors of an item

sql

recursive-ctes

sql-queries

database-performance

byAlex Kataev·Dec 12, 2024

The solution is a recursive Common Table Expression (CTE). Start with the given item's ID as the anchor member. Then join your table to the CTE in a recursion that acts like a time machine, going back in the parent-child relationship.

WITH RECURSIVE Ancestors AS (
    SELECT id, parent_id FROM YourTable WHERE id = {item_id} -- You are here
    UNION ALL
    SELECT yt.id, yt.parent_id FROM YourTable yt
    JOIN Ancestors ON yt.id = Ancestors.parent_id -- DeLorean in action
)
SELECT * FROM Ancestors WHERE id != {item_id}; -- Present is boring, show ancestors!

Replace YourTable and {item_id} with your data.

The CTE Time Machine Explained

Rediscover the alchemy of recursive CTEs. The base case or anchor member is your starting point, your flux capacitor if you will. The recursive member is your DeLorean, revving up to 88mph and travelling up the family tree. It does so by joining the CTE to itself, ancestor by ancestor.

The recursion halts once there aren't any parent_ids left — your flux capacitor has run out of 1.21 gigawatts. So, no infinite loops, just the end of time.

Pit Stops on your Time Travel Adventure

Infinite Recursion: Have an effective flux capacitor (termination condition). In some RDBMS, use SET MAXRECURSION.
Speed: Your DeLorean (id, parent_id used for joining) should have its bolts tightened (indexed) to boost query speed.
Temporal Paradox (Inconsistent Data): Validate for self referencing rows or circular relationships to avoid a never ending journey.

Tweaking your Dashboard (Result Set)

You can use tools like FOR XML PATH('') (in SQL Server) to style your results as a comma-separated string of ancestor IDs.

When in Rome (Database System Specifics)

SQL Server

WITH RECURSIVE is your flux capacitor here. For large trees, OPTION (MAXRECURSION 0) is your unlimited fuel.

PostgreSQL

It's all in the WITH queries here— perfect for jump-starting your time machine.

Oracle

The console here reads Recursive Subquery Factoring. If that wasn't enough, it has the CONNECT BY clause for building family trees.

SQLite

It's got support for recursive CTEs, letting you traverse time streams here too.

Check Before You Rev (Testing and Verification)

Test the time machine using SQLFiddle or an equivalent environment before you jump real timelines. Remember, conditions may vary!

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The CTE Time Machine Explained Pit Stops on your Time Travel Adventure Tweaking your Dashboard (Result Set)When in Rome (Database System Specifics)Check Before You Rev (Testing and Verification)