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I have an MPTT tree of over 100,000 records stored in MySQL using lft, rght and parent_id columns. Now the left/right values became corrupted, while the parent ids are still intact. It would require tons of queries to repair it in the application layer. Is there a good way to put the burden on the database and have it recalculate the left/right values using only SQL?
Just to clarify, I need to recalculate the numeric lft/rght values of a nested set, not the ids of neighboring records.
(source: mysql.com)
353
Here's what I have adapted from @Lieven's answer, incorporating feedback from here for better performance:
DROP PROCEDURE IF EXISTS tree_recover;
DELIMITER //
CREATE PROCEDURE tree_recover ()
MODIFIES SQL DATA
BEGIN
DECLARE currentId, currentParentId CHAR(36);
DECLARE currentLeft INT;
DECLARE startId INT DEFAULT 1;
# Determines the max size for MEMORY tables.
SET max_heap_table_size = 1024 * 1024 * 512;
START TRANSACTION;
# Temporary MEMORY table to do all the heavy lifting in,
# otherwise performance is simply abysmal.
CREATE TABLE `tmp_tree` (
`id` char(36) NOT NULL DEFAULT '',
`parent_id` char(36) DEFAULT NULL,
`lft` int(11) unsigned DEFAULT NULL,
`rght` int(11) unsigned DEFAULT NULL,
PRIMARY KEY (`id`),
INDEX USING HASH (`parent_id`),
INDEX USING HASH (`lft`),
INDEX USING HASH (`rght`)
) ENGINE = MEMORY
SELECT `id`,
`parent_id`,
`lft`,
`rght`
FROM `tree`;
# Leveling the playing field.
UPDATE `tmp_tree`
SET `lft` = NULL,
`rght` = NULL;
# Establishing starting numbers for all root elements.
WHILE EXISTS (SELECT * FROM `tmp_tree` WHERE `parent_id` IS NULL AND `lft` IS NULL AND `rght` IS NULL LIMIT 1) DO
UPDATE `tmp_tree`
SET `lft` = startId,
`rght` = startId + 1
WHERE `parent_id` IS NULL
AND `lft` IS NULL
AND `rght` IS NULL
LIMIT 1;
SET startId = startId + 2;
END WHILE;
# Switching the indexes for the lft/rght columns to B-Trees to speed up the next section, which uses range queries.
DROP INDEX `lft` ON `tmp_tree`;
DROP INDEX `rght` ON `tmp_tree`;
CREATE INDEX `lft` USING BTREE ON `tmp_tree` (`lft`);
CREATE INDEX `rght` USING BTREE ON `tmp_tree` (`rght`);
# Numbering all child elements
WHILE EXISTS (SELECT * FROM `tmp_tree` WHERE `lft` IS NULL LIMIT 1) DO
# Picking an unprocessed element which has a processed parent.
SELECT `tmp_tree`.`id`
INTO currentId
FROM `tmp_tree`
INNER JOIN `tmp_tree` AS `parents`
ON `tmp_tree`.`parent_id` = `parents`.`id`
WHERE `tmp_tree`.`lft` IS NULL
AND `parents`.`lft` IS NOT NULL
LIMIT 1;
# Finding the element's parent.
SELECT `parent_id`
INTO currentParentId
FROM `tmp_tree`
WHERE `id` = currentId;
# Finding the parent's lft value.
SELECT `lft`
INTO currentLeft
FROM `tmp_tree`
WHERE `id` = currentParentId;
# Shifting all elements to the right of the current element 2 to the right.
UPDATE `tmp_tree`
SET `rght` = `rght` + 2
WHERE `rght` > currentLeft;
UPDATE `tmp_tree`
SET `lft` = `lft` + 2
WHERE `lft` > currentLeft;
# Setting lft and rght values for current element.
UPDATE `tmp_tree`
SET `lft` = currentLeft + 1,
`rght` = currentLeft + 2
WHERE `id` = currentId;
END WHILE;
# Writing calculated values back to physical table.
UPDATE `tree`, `tmp_tree`
SET `tree`.`lft` = `tmp_tree`.`lft`,
`tree`.`rght` = `tmp_tree`.`rght`
WHERE `tree`.`id` = `tmp_tree`.`id`;
COMMIT;
DROP TABLE `tmp_tree`;
END//
DELIMITER ;
Worked well with some test data, but it's still running on my 100,000 records tree, so I can't give any final judgement yet. The naïve script working directly on the physical table has abysmal performance, running for at least hours, more likely days. Switching to a temporary MEMORY table brought this time down to about an hour, choosing the right indexes cut it down to 10 mins.
140
Using SQL Server, following script seems to be working for me.
category_id name parent lft rgt lftcalc rgtcalc
----------- -------------------- ----------- ----------- ----------- ----------- -----------
1 ELECTRONICS NULL 1 20 1 20
2 TELEVISIONS 1 2 9 2 9
3 TUBE 2 3 4 3 4
4 LCD 2 5 6 5 6
5 PLASMA 2 7 8 7 8
6 PORTABLE ELECTRONICS 1 10 19 10 19
7 MP3 PLAYERS 6 11 14 11 14
8 FLASH 7 12 13 12 13
9 CD PLAYERS 6 15 16 15 16
10 2 WAY RADIOS 6 17 18 17 18
SET NOCOUNT ON
GO
DECLARE @nested_category TABLE (
category_id INT PRIMARY KEY,
name VARCHAR(20) NOT NULL,
parent INT,
lft INT,
rgt INT
);
DECLARE @current_Category_ID INTEGER
DECLARE @current_parent INTEGER
DECLARE @SafeGuard INTEGER
DECLARE @myLeft INTEGER
SET @SafeGuard = 100
INSERT INTO @nested_category
SELECT 1,'ELECTRONICS',NULL,NULL,NULL
UNION ALL SELECT 2,'TELEVISIONS',1,NULL,NULL
UNION ALL SELECT 3,'TUBE',2,NULL,NULL
UNION ALL SELECT 4,'LCD',2,NULL,NULL
UNION ALL SELECT 5,'PLASMA',2,NULL,NULL
UNION ALL SELECT 6,'PORTABLE ELECTRONICS',1,NULL,NULL
UNION ALL SELECT 7,'MP3 PLAYERS',6,NULL,NULL
UNION ALL SELECT 8,'FLASH',7,NULL,NULL
UNION ALL SELECT 9,'CD PLAYERS',6,NULL,NULL
UNION ALL SELECT 10,'2 WAY RADIOS',6,NULL,NULL
/* Initialize */
UPDATE @nested_category
SET lft = 1
, rgt = 2
WHERE parent IS NULL
UPDATE @nested_category
SET lft = NULL
, rgt = NULL
WHERE parent IS NOT NULL
WHILE EXISTS (SELECT * FROM @nested_category WHERE lft IS NULL) AND @SafeGuard > 0
BEGIN
SELECT @current_Category_ID = MAX(nc.category_id)
FROM @nested_category nc
INNER JOIN @nested_category nc2 ON nc2.category_id = nc.parent
WHERE nc.lft IS NULL
AND nc2.lft IS NOT NULL
SELECT @current_parent = parent
FROM @nested_category
WHERE category_id = @current_category_id
SELECT @myLeft = lft
FROM @nested_category
WHERE category_id = @current_parent
UPDATE @nested_category SET rgt = rgt + 2 WHERE rgt > @myLeft;
UPDATE @nested_category SET lft = lft + 2 WHERE lft > @myLeft;
UPDATE @nested_category SET lft = @myLeft + 1, rgt = @myLeft + 2 WHERE category_id = @current_category_id
SET @SafeGuard = @SafeGuard - 1
END
SELECT * FROM @nested_category ORDER BY category_id
SELECT COUNT(node.name), node.name, MIN(node.lft)
FROM @nested_category AS node,
@nested_category AS parent
WHERE node.lft BETWEEN parent.lft AND parent.rgt
GROUP BY
node.name
ORDER BY
3, 1
SET NOCOUNT ON
GO
DECLARE @nested_category TABLE (
category_id INT PRIMARY KEY,
name VARCHAR(20) NOT NULL,
parent INT,
lft INT,
rgt INT,
lftcalc INT,
rgtcalc INT
);
INSERT INTO @nested_category
SELECT 1,'ELECTRONICS',NULL,1,20,NULL,NULL
UNION ALL SELECT 2,'TELEVISIONS',1,2,9,NULL,NULL
UNION ALL SELECT 3,'TUBE',2,3,4,NULL,NULL
UNION ALL SELECT 4,'LCD',2,5,6,NULL,NULL
UNION ALL SELECT 5,'PLASMA',2,7,8,NULL,NULL
UNION ALL SELECT 6,'PORTABLE ELECTRONICS',1,10,19,NULL,NULL
UNION ALL SELECT 7,'MP3 PLAYERS',6,11,14,NULL,NULL
UNION ALL SELECT 8,'FLASH',7,12,13,NULL,NULL
UNION ALL SELECT 9,'CD PLAYERS',6,15,16,NULL,NULL
UNION ALL SELECT 10,'2 WAY RADIOS',6,17,18,NULL,NULL
/* Initialize */
UPDATE @nested_category
SET lftcalc = 1
, rgtcalc = 2
WHERE parent IS NULL
DECLARE @current_Category_ID INTEGER
DECLARE @current_parent INTEGER
DECLARE @SafeGuard INTEGER
DECLARE @myRight INTEGER
DECLARE @myLeft INTEGER
SET @SafeGuard = 100
WHILE EXISTS (SELECT * FROM @nested_category WHERE lftcalc IS NULL) AND @SafeGuard > 0
BEGIN
SELECT @current_Category_ID = MAX(nc.category_id)
FROM @nested_category nc
INNER JOIN @nested_category nc2 ON nc2.category_id = nc.parent
WHERE nc.lftcalc IS NULL
AND nc2.lftcalc IS NOT NULL
SELECT @current_parent = parent
FROM @nested_category
WHERE category_id = @current_category_id
SELECT @myLeft = lftcalc
FROM @nested_category
WHERE category_id = @current_parent
UPDATE @nested_category SET rgtcalc = rgtcalc + 2 WHERE rgtcalc > @myLeft;
UPDATE @nested_category SET lftcalc = lftcalc + 2 WHERE lftcalc > @myLeft;
UPDATE @nested_category SET lftcalc = @myLeft + 1, rgtcalc = @myLeft + 2 WHERE category_id = @current_category_id
SELECT * FROM @nested_category WHERE category_id = @current_parent
SELECT * FROM @nested_category ORDER BY category_id
SET @SafeGuard = @SafeGuard - 1
END
SELECT * FROM @nested_category ORDER BY category_id
SELECT COUNT(node.name), node.name, MIN(node.lft)
FROM @nested_category AS node,
@nested_category AS parent
WHERE node.lft BETWEEN parent.lft AND parent.rgt
GROUP BY
node.name
ORDER BY
3, 1
You are rescue me!!! I use mixed tree model, so when the day is coming, my tree (30000+) was corrupted. I learn from both of your tech, but is not recovery, just fully rebuild with lost all of sorting and reverse tree... I think, need to keep in mind older cat_left.... Just for possible integrity. So, it maybe looks like...
DROP PROCEDURE IF EXISTS tree_recover;
DELIMITER |
CREATE PROCEDURE tree_recover ()
MODIFIES SQL DATA
BEGIN
DECLARE currentId, currentParentId CHAR(36);
DECLARE currentLeft INT;
DECLARE startId INT DEFAULT 1;
# Determines the max size for MEMORY tables.
SET max_heap_table_size = 1024 * 1024 * 512;
START TRANSACTION;
# Temporary MEMORY table to do all the heavy lifting in,
# otherwise performance is simply abysmal.
DROP TABLE IF EXISTS `tmp_cat`;
CREATE TABLE `tmp_cat` (
`cat_id` char(36) NOT NULL DEFAULT '',
`cat_parent` char(36) DEFAULT NULL,
`cat_left` int(11) unsigned DEFAULT NULL,
`cat_right` int(11) unsigned DEFAULT NULL,
`cat_left_old` int(11) unsigned DEFAULT NULL,
PRIMARY KEY (`cat_id`),
INDEX USING HASH (`cat_parent`),
INDEX USING HASH (`cat_left`),
INDEX USING HASH (`cat_right`),
INDEX USING HASH (`cat_left_old`)
) ENGINE = MEMORY
SELECT `cat_id`,
`cat_parent`,
`cat_left`,
`cat_right`,
`cat_left` as cat_left_old
FROM `catalog`;
# Leveling the playing field.
UPDATE `tmp_cat`
SET `cat_left` = NULL,
`cat_right` = NULL;
# Establishing starting numbers for all root elements.
WHILE EXISTS (SELECT * FROM `tmp_cat` WHERE `cat_parent` IS NULL AND `cat_left` IS NULL AND `cat_right` IS NULL ORDER BY cat_left_old LIMIT 1) DO
UPDATE `tmp_cat`
SET `cat_left` = startId,
`cat_right` = startId + 1
WHERE `cat_parent` IS NULL
AND `cat_left` IS NULL
AND `cat_right` IS NULL
LIMIT 1;
SET startId = startId + 2;
END WHILE;
# Switching the indexes for the cat_left/rght columns to B-Trees to speed up the next section, which uses range queries.
DROP INDEX `cat_left` ON `tmp_cat`;
DROP INDEX `cat_right` ON `tmp_cat`;
DROP INDEX `cat_left_old` ON `tmp_cat`;
CREATE INDEX `cat_left` USING BTREE ON `tmp_cat` (`cat_left`);
CREATE INDEX `cat_right` USING BTREE ON `tmp_cat` (`cat_right`);
CREATE INDEX `cat_left_old` USING BTREE ON `tmp_cat` (`cat_left_old`);
# Numbering all child elements
WHILE EXISTS (SELECT * FROM `tmp_cat` WHERE `cat_left` IS NULL ORDER BY cat_left_old LIMIT 1) DO
# Picking an unprocessed element which has a processed parent.
SELECT `tmp_cat`.`cat_id`
INTO currentId
FROM `tmp_cat`
INNER JOIN `tmp_cat` AS `parents`
ON `tmp_cat`.`cat_parent` = `parents`.`cat_id`
WHERE `tmp_cat`.`cat_left` IS NULL
AND `parents`.`cat_left` IS NOT NULL
ORDER BY `tmp_cat`.cat_left_old DESC
LIMIT 1;
# Finding the element's parent.
SELECT `cat_parent`
INTO currentParentId
FROM `tmp_cat`
WHERE `cat_id` = currentId;
# Finding the parent's cat_left value.
SELECT `cat_left`
INTO currentLeft
FROM `tmp_cat`
WHERE `cat_id` = currentParentId;
# Shifting all elements to the right of the current element 2 to the right.
UPDATE `tmp_cat`
SET `cat_right` = `cat_right` + 2
WHERE `cat_right` > currentLeft;
UPDATE `tmp_cat`
SET `cat_left` = `cat_left` + 2
WHERE `cat_left` > currentLeft;
# Setting cat_left and rght values for current element.
UPDATE `tmp_cat`
SET `cat_left` = currentLeft + 1,
`cat_right` = currentLeft + 2
WHERE `cat_id` = currentId;
END WHILE;
# Writing calculated values back to physical table.
UPDATE `catalog`, `tmp_cat`
SET `catalog`.`cat_left` = `tmp_cat`.`cat_left`,
`catalog`.`cat_right` = `tmp_cat`.`cat_right`
WHERE `catalog`.`cat_id` = `tmp_cat`.`cat_id`;
COMMIT;
DROP TABLE IF EXISTS `tmp_cat`;
END|
4
In all solutions provided, I was getting a problem where MySQL would prompt that it would be Running query for hours but nothing would happen.
I then realized that if I set the lft and rght values to 1 and 2 in the first record of the tmp_tree table (the one with parent_id = 0), everything worked fine. Maybe the procedure needs updating to do this automatically.
1
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