Thread: Tree structure index usage

I have a tree structure like:

CREATE TABLE my_tree (id SERIAL PRIMARY KEY,dir INTEGER references my_tree ON DELETE CASCADE ON UPDATE CASCADE,name
TEXT,UNIQUE(name,dir)
 
);

Then I have a function is_parent(integer, integer), it will tell you if the second integer (id) is a sub directory of
thefirst (regardless of the number of levels).
 

now obviously is_parent  does some queries itself.

and someone may choose to update the dir value of a row.

is there any way I can create an efficient index on this structure/function?

The only way I have come up with, is to create an auxilliary table which basically looks like this:

CREATE TABLE my_tree_is_parent (is_parent boolean,dir INTEGER REFERENCES my_tree,id INTEGER,PRIMARY KEY (dir, id)
);

and the appropriate triggers to populate and update the table according to modifications in my_tree, however, albeit
givingsome performance increase (in some cases), it complicates the queries a lot and makes the whole system a lot less
userfriendly.

any ideas?

Regards,

Aasmund Midttun Godal

aasmund@godal.com - http://www.godal.com/
+47 40 45 20 46

Aasmund,

> CREATE TABLE my_tree (
>  id SERIAL PRIMARY KEY,
>  dir INTEGER references my_tree ON DELETE CASCADE ON UPDATE CASCADE,
>  name TEXT,
>  UNIQUE(name, dir)
> );
> 
> Then I have a function is_parent(integer, integer), it will tell you
> if the second integer (id) is a sub directory of the first
> (regardless of the number of levels).
> 
> now obviously is_parent  does some queries itself.
> 
> and someone may choose to update the dir value of a row.
> 
> is there any way I can create an efficient index on this
> structure/function?

Hmmm.  Seperate indexes on ID and DIR should be sufficient for most
purposes.  More complex approaches are only likely to slow things down.
How many records do you have?  How many levels to the tree structure?

For an excellent discussion of efficient construction and queryin of
tree structures, see Joe Celko's "SQL for Smarties."

-Josh

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