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Trees are special cases of graphs. They are acyclic i.e. there is at most one path from any node to any other node. Typical uses include hierarchical data (parent-child relationships; roll-up aggregate values) and BTree indexes.

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I've got table like this in postgres: id primary key parent_id foreign key on id some data columns I need no a constrain which prevents cycles on the parent relations. There might be more tree in the table (root of a tree is null in parent_id). How to achieve this goal? Thanks Daniel …
asked Jan 7 '15 by dve