From: greg@turnstep.com
To: pgsql-sql@postgresql.org
Cc: 
Subject: Re: celko nested set functions
Date: Mon, 25 Nov 2002 20:22:34 -0000
Message-ID: <479891932701b5829f621f49d602a69a@biglumber.com>


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Robert Treat and I came up with a better way to move 
nodes from one branch to another inside of a nested tree:


CREATE or REPLACE FUNCTION move_tree (integer, integer) RETURNS text
AS '

-- Moves part of a nested set tree to another part.
-- Pass in the left of the child (from) and the left of the parent (to)

DECLARE

cleft INTEGER;     cright INTEGER;
pleft INTEGER;     pright INTEGER;
leftbound INTEGER; rightbound INTEGER;
treeshift INTEGER; cwidth INTEGER;
leftrange INTEGER; rightrange INTEGER;

BEGIN

-- Self-move makes no sense
IF $1 = $2 THEN
  RETURN ''Cannot move: entries are identical'';
END IF;

SELECT lft, rgt FROM tree WHERE lft = $1 INTO cleft, cright;
SELECT lft, rgt FROM tree WHERE lft = $2 INTO pleft, pright;

-- Make sure the child exists
IF cleft IS NULL THEN
  RETURN ''No entry found with an left of ''||$1;
END IF;

-- Make sure the parent exists
IF pleft IS NULL THEN
  RETURN ''No entry found with a left of ''||$2;
END IF;

-- Parent cannot be underneath the child
IF pleft BETWEEN cleft AND cright THEN
  RETURN ''Cannot move: first entry contains second'';
END IF;

-- Child may already be in the proper place
IF cleft = pleft+1 THEN
  RETURN ''No changes need to be made'';
END IF;

IF cleft > pleft THEN 
  treeshift  := pleft - cleft + 1;
  leftbound  := pleft+1;
  rightbound := cleft-1;
  cwidth     := cright-cleft+1;
  leftrange := cright;
  rightrange  := pleft;
ELSE
  treeshift  := pleft - cright;
  leftbound  := cright + 1;
  rightbound := pleft;
  cwidth     := cleft-cright-1;
  leftrange  := pleft+1;
  rightrange := cleft;
END IF;


UPDATE tree
  SET lft = CASE
            WHEN lft BETWEEN leftbound AND rightbound THEN lft + cwidth
            WHEN lft BETWEEN cleft AND cright THEN lft + treeshift
            ELSE lft END,
      rgt = CASE
            WHEN rgt BETWEEN leftbound AND rightbound THEN rgt + cwidth
            WHEN rgt BETWEEN cleft AND cright THEN rgt + treeshift
            ELSE rgt END
WHERE lft < leftrange OR rgt > rightrange;

RETURN ''Tree has been moved'';

END;
'
LANGUAGE 'plpgsql';


Greg Sabino Mullane greg@turnstep.com
PGP Key: 0x14964AC8 200211251526

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