Optimized SQL for tree structures

Question

How would you get tree-structured data from a database with the best performance? For example, say you have a folder-hierarchy in a database. Where the folder-database-row h

Answer 1

Celko wrote about this (2000):

http://www.dbmsmag.com/9603d06.html

http://www.intelligententerprise.com/001020/celko1_1.jhtml;jsessionid=3DFR02341QLDEQSNDLRSKHSCJUNN2JVN?_requestid=32818

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and other people asked:

Joining other tables in oracle tree queries

How to calculate the sum of values in a tree using SQL

How to store directory / hierarchy / tree structure in the database?

Performance of recursive stored procedures in MYSQL to get hierarchical data

What is the most efficient/elegant way to parse a flat table into a tree?

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finally, you could look at the rails "acts_as_tree" (read-heavy) and "acts_as_nested_set" (write-heavy) plugins. I don't ahve a good link comparing them.