in reply to Re^3: (OT?) Recursive sql queries?
in thread (OT?) Recursive sql queries?

Well, the accessing sql is refreshingly simple, but the updating code 
BEGIN
DECLARE right_most_sibling INTEGER;

SET right_most_sibling
    = (SELECT rgt
         FROM Personnel
        WHERE emp = :your_boss);

UPDATE Personnel
   SET lft = CASE WHEN lft > right_most_sibling
                  THEN lft + 2
                  ELSE lft END,
       rgt = CASE WHEN rgt >= right_most_sibling
                  THEN rgt + 2
                  ELSE rgt END
 WHERE rgt >= right_most_sibling;

INSERT INTO Personnel (emp, lft, rgt)
VALUES ('New Guy', right_most_sibling,
                  (right_most_sibling + 1))
END;

[download]
Is rather scary and I'm not even sure my database (mysql) supports those.

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Re: Re: Re^3: (OT?) Recursive sql queries?
by geekbunker (Acolyte) on Mar 02, 2004 at 09:47 UTC
    This translates to MySQL, tested on 4.0.18: 
     SELECT @right_most_sibling := rgt
   FROM Personnel
  WHERE emp = ? /* :your_boss */;

 UPDATE Personnel
    SET lft = IF(lft >  @right_most_sibling, lft + 2, lft),
        rgt = IF(rgt >= @right_most_sibling, rgt + 2, rgt)
  WHERE rgt >= @right_most_sibling;

 INSERT INTO Personnel (emp, lft, rgt)
 VALUES ('New Guy', @right_most_sibling, @right_most_sibling + 1);

    [download]
    I don't know what version of MySQL introduced the @var := doohickey. Be warned that inserts etc. into a nested-set must touch all nodes to the right of the parent. That shouldn't be a problem if the tree is small or updated infrequently. A smarty might be able to devise a method to mitigate the change, but I'm not so smart, I plan to brute force a solution one of these days. :-) This nested-set thread has piqued my interest in the subject.
[reply]
[d/l]

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