Move node in nested set

Question

I\'d need a MySQL query that moves a node and all its children within a nested set. I found this site, but that function just seems so illogical - there\'s no universe

Answer 1

There are many answers already, but I feel like mine can be useful for someone. Based on answer of Roger Keays (thank you very much!), I wrote stored procedures for mySQL database:

-- to move target before specified node
CREATE DEFINER=`root`@`%` PROCEDURE `move_before`(IN target_id int, before_id int)
BEGIN
    SELECT @new_pos := lft FROM dirs WHERE  id = before_id; 
    CALL  move(target_id, @new_pos);
END

-- to move target after specified node
CREATE DEFINER=`root`@`%` PROCEDURE `move_after`(IN target_id int, after_id int)
BEGIN
    SELECT @new_pos := rgt + 1 FROM dirs WHERE  id = after_id;
    CALL  move(target_id, @new_pos);
END

-- to move target to the specified node
CREATE DEFINER=`root`@`%` PROCEDURE `move_in`(IN target_id int, parent_id int)
BEGIN
    SELECT @new_pos := rgt FROM dirs WHERE  id = parent_id;
    CALL  move(target_id, @new_pos);
END

--main procedure to move target before position 
CREATE DEFINER=`root`@`%` PROCEDURE `move`(in target_id int, in  new_pos int)
BEGIN

    SELECT @oldlft :=  lft, @oldrgt :=  rgt 
    FROM dirs 
    WHERE target_id =  id;

    SET @width := @oldrgt - @oldlft +1;
    SET @distance :=  new_pos - @oldlft;
    SET @tmppos := @oldlft;

    IF (@distance <0)
    THEN
        SELECT @distance := @distance - @width;
        SELECT @tmppos := @tmppos + @width;
    END IF;

    -- create new space for subtree
    UPDATE dirs SET lft = lft + @width WHERE lft >=  new_pos;
    UPDATE dirs SET rgt = rgt + @width WHERE rgt >=  new_pos;

    -- move subtree into new space
    UPDATE dirs SET lft = lft + @distance, rgt = rgt + @distance
        WHERE lft >= @tmppos AND rgt < @tmppos + @width;

    -- remove old space vacated by subtree
    UPDATE dirs SET lft = lft - @width WHERE lft > @oldrgt;
    UPDATE dirs SET rgt = rgt - @width WHERE rgt > @oldrgt;

END