On Sunday 24. January 2010 16.22.00 Wayne E. Pfeffer wrote: > If you do not use null to represent a root node, when you go to unwind the > data from the table to generate a hierarchy tree, you could end up with an > infinite loop. The query will always be looking for the next parent in the > hierarchy. Meaning, you will want to find the parent of a node using the > given parent_id, the query will find the parent of 1 to be 1, then it will > look again for the parent of 1 it will find 1, etc. etc. ad nauseum. I enjoy > using recursion as much as the next guy, but this could cause some serious > issues with the PostgreSQL query engine eating up system resources. It doesn't really matter if the root node is NULL or 0 or whatever. You just have to realize that the root node is a special case and program accordingly. An adjacency tree is not a normalized structure, and will never be. It's the programmer's responsibility to ensure that circular references can't occur. regards, -- Leif Biberg Kristensen http://solumslekt.org/ -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
