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Editorial Team
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Asked: 2026-05-20T10:28:36+00:00

I have a tree structure in MySQL using a parent_id field for each node.

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I have a tree structure in MySQL using a parent_id field for each node. The structure is quite large but only about 8 levels deep. Each node also has a child_counter field.

I’m looking for a performant way to calculate (and update) the number of children each node has (by children I am including children of children etc.), preferably with not too many SQL calls. I don’t expect this to be super fast, just good enough.

I’m hoping there might be some way to do a mass update as the algorithm iterates.

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1 Answer

  1. Editorial Team

    I’ve implemented something like this before, but not quite. Are you able to store a “depth” integer on each node, to mark their depth in the tree? If so, you could do this with 8 queries, which if properly indexed would be quite reasonable. Something like this I think (don’t have mysql handy). You would query from the lowest depth (i.e. 8) upwards:
    UPDATE Node SET child_counter = ((SELECT SUM(child_counter) FROM Node WHERE parent_id = id) + (SELECT COUNT(0) FROM Node WHERE parent_id = id)) WHERE depth = x

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