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POMySQL Closure Table hierarchical database - How to pull information out in the correct order
 

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    <p>I have a MySQL database holding hierarchical data using the Closure Table method. A simple sample database create script follows the question. My issue at the moment is how do I pull data out of the database in the correct order? I'm currently using the following select statement.</p> <pre><code>SELECT `TreeData`.`iD`, `TreeData`.`subsectionOf`, CONCAT(REPEAT('-', `TreePaths`.`len`),`TreeData`.`name`), `TreePaths`.`len`,`TreePaths`.`ancestor`,`TreePaths`.`descendant` FROM `TreeData` LEFT JOIN `TreePaths` ON `TreeData`.`iD` = `TreePaths`.`descendant` WHERE `TreePaths`.`ancestor` = 1 ORDER BY `TreeData`.`subsectionOrder` </code></pre> <p>It pulls the correct information but not in the correct order.</p> <p>The sample database create script with sample data.</p> <pre><code>-- Simple Sample SET FOREIGN_KEY_CHECKS=0; DROP TRIGGER IF EXISTS Tree_Insert; DROP TRIGGER IF EXISTS Tree_Update; DROP TABLE IF EXISTS TreePaths; DROP TABLE IF EXISTS TreeData; SET FOREIGN_KEY_CHECKS=1; CREATE TABLE `TreeData` ( `iD` INT NOT NULL, -- PK `subsectionOf` INT, -- Parent ID &amp; FK `subsectionOrder` INT, -- Oder of Subsections `name` NVARCHAR(500) NOT NULL, -- Name for the entry PRIMARY KEY (`iD`), FOREIGN KEY (`subsectionOf`) REFERENCES TreeData(`iD`) ON DELETE CASCADE, INDEX(`name`) ) ENGINE = MYISAM; -- Trigger to update the EntryPaths table for new entries DELIMITER // CREATE TRIGGER `Tree_Insert` AFTER INSERT ON `TreeData` FOR EACH ROW BEGIN INSERT INTO `TreePaths` (`ancestor`, `descendant`, `len`) SELECT `ancestor`, NEW.`iD`, len + 1 FROM `TreePaths` WHERE `descendant` = NEW.`subsectionOf` UNION ALL SELECT NEW.`iD`, NEW.`iD`, 0; END; // DELIMITER ; DELIMITER // CREATE TRIGGER `Tree_Update` BEFORE UPDATE ON `TreeData` FOR EACH ROW BEGIN -- From http://www.mysqlperformanceblog.com/2011/02/14/moving-subtrees-in-closure-table/ IF OLD.`subsectionOf` != NEW.`subsectionOf` THEN -- Remove the node from its current parent DELETE a FROM `TreePaths` AS a JOIN `TreePaths` AS d ON a.`descendant` = d.`descendant` LEFT JOIN `TreePaths` AS x ON x.`ancestor` = d.`ancestor` AND x.`descendant` = a.`ancestor` WHERE d.`ancestor` = OLD.`iD` AND x.`ancestor` IS NULL; -- Add the node to its new parent INSERT `TreePaths` (`ancestor`, `descendant`, `len`) SELECT supertree.`ancestor`, subtree.`descendant`, supertree.`len`+subtree.`len`+1 FROM `TreePaths` AS supertree JOIN `TreePaths` AS subtree WHERE subtree.`ancestor` = OLD.`iD` AND supertree.`descendant` = NEW.`subsectionOf`; END IF; END; // DELIMITER ; CREATE TABLE `TreePaths` ( `ancestor` INT NOT NULL, `descendant` INT NOT NULL, `len` INT NOT NULL, PRIMARY KEY (`ancestor`, `descendant`), FOREIGN KEY (`ancestor`) REFERENCES TreeData(`iD`) ON DELETE CASCADE, FOREIGN KEY (`descendant`) REFERENCES TreeData(`iD`) ON DELETE CASCADE ) ENGINE = MYISAM; INSERT INTO `TreeData` VALUES(1, NULL, NULL, 'Root A'); INSERT INTO `TreeData` VALUES(2, 1, 1, 'Item 1'); INSERT INTO `TreeData` VALUES(3, 1, 2, 'Item 2'); INSERT INTO `TreeData` VALUES(4, 1, 3, 'Item 3'); INSERT INTO `TreeData` VALUES(5, 2, 2, 'Item 1 Sub Item 2'); INSERT INTO `TreeData` VALUES(6, 2, 1, 'Item 1 Sub Item 1'); INSERT INTO `TreeData` VALUES(7, 1, 3, 'Item 4'); INSERT INTO `TreeData` VALUES(8, 4, 1, 'Item 3 Sub Item 1'); INSERT INTO `TreeData` VALUES(9, 4, 2, 'Item 3 Sub Item 2'); INSERT INTO `TreeData` VALUES(10, NULL, NULL, 'Root B'); INSERT INTO `TreeData` VALUES(11, 10, 1, 'Item A'); INSERT INTO `TreeData` VALUES(12, 10, 2, 'Item B'); INSERT INTO `TreeData` VALUES(13, 10, 3, 'Item C'); </code></pre>
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