Rekursive Abfrage für die Adjazenzliste zum Traversieren des Baums in SQL?

Question

Ich bin dabei, Daten von einem Datenbankschema in ein anderes zu migrieren. Das alte Schema hat ein Kategorisierungssystem, das auf einer Adjazenzliste basiert, mit id, Kategorie und parent_id. Wenn eine Kategorie unter einer zweiten liegt, hat diese Kategorie die ID der zweiten Kategorie als ihre übergeordnete ID. Zum Beispiel:

+-------------+----------------------+--------+
| category_id | name                 | parent |
+-------------+----------------------+--------+
|           1 | ELECTRONICS          |   NULL |
|           2 | TELEVISIONS          |      1 |
|           3 | TUBE                 |      2 |
|           4 | LCD                  |      2 |
|           5 | PLASMA               |      2 |
|           6 | PORTABLE ELECTRONICS |      1 |
|           7 | MP3 PLAYERS          |      6 |
|           8 | FLASH                |      7 |
|           9 | CD PLAYERS           |      6 |
|          10 | 2 WAY RADIOS         |      6 |
+-------------+----------------------+--------+

Das neue Schema verfügt über einen geänderten Algorithmus für das Traversieren des Preorder-Baums:

+-------------+----------------------+-----+-----+
| category_id | name                 | lft | rgt |
+-------------+----------------------+-----+-----+
|           1 | ELECTRONICS          |   1 |  20 |
|           2 | TELEVISIONS          |   2 |   9 |
|           3 | TUBE                 |   3 |   4 |
|           4 | LCD                  |   5 |   6 |
|           5 | PLASMA               |   7 |   8 |
|           6 | PORTABLE ELECTRONICS |  10 |  19 |
|           7 | MP3 PLAYERS          |  11 |  14 |
|           8 | FLASH                |  12 |  13 |
|           9 | CD PLAYERS           |  15 |  16 |
|          10 | 2 WAY RADIOS         |  17 |  18 |
+-------------+----------------------+-----+-----+

Beispiele aus dem Artikel Hierarchische Daten in MySQL verwalten .

Wie auch immer, ich bin in der Lage, ein PHP-Skript mit einer rekursiven Funktion zu schreiben zu schreiben, die die Adjazenzliste in die Preorder-Baumstruktur überführt. Grundsätzlich wird für jede Zeile ein leerer 'rgt'-Wert eingefügt, nach Kindern gesucht nach Kindern und wendet die Funktion rekursiv auf sie an, wobei es die den Zähler und aktualisiert dann den 'rgt'-Wert.

Aber ich möchte dies in reinem SQL tun. Allerdings weiß ich nicht genug, um um damit Fuß zu fassen. Zunächst einmal weiß ich nicht, ob man dies mit einer rekursiven Abfrage machen kann, oder ob es andere Möglichkeiten gibt, dies zu tun.

Answer 1

Es handelt sich um ein Beispiel, das verallgemeinert oder an Ihre Situation angepasst werden kann.

Zunächst werde ich eine Adjazenzliste erstellen (Sprachfamiliendaten aus Wikipedia):

CREATE TABLE IF NOT EXISTS `language_family_adj_list` (
  `language_id` int(11) NOT NULL auto_increment,
  `language` varchar(20) NOT NULL,
  `parent_id` int(11) default NULL,
  PRIMARY KEY  (`language_id`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 AUTO_INCREMENT=41 ;

INSERT INTO `language_family_adj_list` (`language_id`, `language`, `parent_id`) VALUES
(1, 'Finno-Ugric', NULL),
(2, 'Hungarian', 1),
(3, 'Khanty', 1),
(4, 'Mansi', 1),
(5, 'Permic', 1),
(6, 'Mari', 1),
(7, 'Mordvinic', 1),
(8, 'Sami', 1),
(9, 'Baltic-Finnic', 1),
(10, 'Komi', 5),
(11, 'Komi-Permyak', 5),
(12, 'Udmurt', 5),
(13, 'Erzya', 7),
(14, 'Moksha', 7),
(15, 'Western Sami', 8),
(16, 'Eastern Sami', 8),
(17, 'Southern Sami', 15),
(18, 'Umi Sami', 15),
(19, 'Lule Sami', 15),
(20, 'Pite Sami', 15),
(22, 'Northern Sami', 15),
(23, 'Kemi Sami', 16),
(24, 'Inari Sami', 16),
(25, 'Akkala Sami', 16),
(26, 'Kildin Sami', 16),
(27, 'Skolt Sami', 16),
(28, 'Ter Sami', 16),
(29, 'Estonian', 9),
(30, 'Finnish', 9),
(31, 'Ingrian', 9),
(32, 'Karelian', 9),
(33, 'Livonian', 9),
(34, 'Veps', 9),
(35, 'Votic', 9),
(36, 'South Estonian', 29),
(37, 'Voro', 36),
(38, 'Karelian Proper', 32),
(39, 'Lude', 32),
(40, 'Olonets Karelian', 32);

Hier ist eine Abfrage zur Veranschaulichung:

mysql> SELECT t1.language AS lev1, t2.language as lev2, t3.language as lev3, t4.language as lev4, t5.language AS lev5
    -> FROM language_family_adj_list AS t1
    -> LEFT JOIN language_family_adj_list AS t2 ON t2.parent_id = t1.language_id
    -> LEFT JOIN language_family_adj_list AS t3 ON t3.parent_id = t2.language_id
    -> LEFT JOIN language_family_adj_list AS t4 ON t4.parent_id = t3.language_id
    -> LEFT JOIN language_family_adj_list AS t5 ON t5.parent_id = t4.language_id
    -> WHERE t1.parent_id IS NULL
    -> ORDER BY t1.language, t2.language, t3.language, t4.language, t5.language;
+-------------+---------------+--------------+------------------+------+
| lev1        | lev2          | lev3         | lev4             | lev5 |
+-------------+---------------+--------------+------------------+------+
| Finno-Ugric | Baltic-Finnic | Estonian     | South Estonian   | Voro | 
| Finno-Ugric | Baltic-Finnic | Finnish      | NULL             | NULL | 
| Finno-Ugric | Baltic-Finnic | Ingrian      | NULL             | NULL | 
| Finno-Ugric | Baltic-Finnic | Karelian     | Karelian Proper  | NULL | 
| Finno-Ugric | Baltic-Finnic | Karelian     | Lude             | NULL | 
| Finno-Ugric | Baltic-Finnic | Karelian     | Olonets Karelian | NULL | 
| Finno-Ugric | Baltic-Finnic | Livonian     | NULL             | NULL | 
| Finno-Ugric | Baltic-Finnic | Veps         | NULL             | NULL | 
| Finno-Ugric | Baltic-Finnic | Votic        | NULL             | NULL | 
| Finno-Ugric | Hungarian     | NULL         | NULL             | NULL | 
| Finno-Ugric | Khanty        | NULL         | NULL             | NULL | 
| Finno-Ugric | Mansi         | NULL         | NULL             | NULL | 
| Finno-Ugric | Mari          | NULL         | NULL             | NULL | 
| Finno-Ugric | Mordvinic     | Erzya        | NULL             | NULL | 
| Finno-Ugric | Mordvinic     | Moksha       | NULL             | NULL | 
| Finno-Ugric | Permic        | Komi         | NULL             | NULL | 
| Finno-Ugric | Permic        | Komi-Permyak | NULL             | NULL | 
| Finno-Ugric | Permic        | Udmurt       | NULL             | NULL | 
| Finno-Ugric | Sami          | Eastern Sami | Akkala Sami      | NULL | 
| Finno-Ugric | Sami          | Eastern Sami | Inari Sami       | NULL | 
| Finno-Ugric | Sami          | Eastern Sami | Kemi Sami        | NULL | 
| Finno-Ugric | Sami          | Eastern Sami | Kildin Sami      | NULL | 
| Finno-Ugric | Sami          | Eastern Sami | Skolt Sami       | NULL | 
| Finno-Ugric | Sami          | Eastern Sami | Ter Sami         | NULL | 
| Finno-Ugric | Sami          | Western Sami | Lule Sami        | NULL | 
| Finno-Ugric | Sami          | Western Sami | Northern Sami    | NULL | 
| Finno-Ugric | Sami          | Western Sami | Pite Sami        | NULL | 
| Finno-Ugric | Sami          | Western Sami | Southern Sami    | NULL | 
| Finno-Ugric | Sami          | Western Sami | Umi Sami         | NULL | 
+-------------+---------------+--------------+------------------+------+
29 rows in set (0.00 sec)

Hier ist also das geänderte Schema der Preorder-Traversal-Tabelle:

CREATE TABLE language_family_mptt (
 language VARCHAR(30) NOT NULL,
 lft INT NOT NULL,
 rgt INT NOT NULL
) COLLATE utf8;

Und hier ist die rekursive gespeicherte Prozedur, um die Daten zu migrieren:

TRUNCATE TABLE language_family_mptt;
SET max_sp_recursion_depth = 255;
DROP PROCEDURE IF EXISTS insert_branches;
DROP PROCEDURE IF EXISTS start_tree;
DELIMITER ~~

CREATE PROCEDURE start_tree()
BEGIN
    DECLARE language_field VARCHAR(100);
    DECLARE done INT DEFAULT 0;
    DECLARE insert_id INT;
    DECLARE source_id INT;

    DECLARE cursor1 CURSOR FOR SELECT language, language_id FROM language_family_adj_list WHERE parent_id IS NULL ORDER BY language;

    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;

    OPEN cursor1;
    read_loop: LOOP

        SET @my_left = 1;

        FETCH cursor1 INTO language_field, source_id;
        INSERT INTO language_family_mptt ( language, lft ) VALUES ( language_field, 1 );

        CALL insert_branches( source_id );

        UPDATE language_family_mptt SET rgt = @my_left + 1 WHERE lft = 1 AND rgt = 0;

        IF done THEN
            LEAVE read_loop;
        END IF;

    END LOOP;
    CLOSE cursor1;

END; ~~

CREATE PROCEDURE insert_branches( IN source_parent_id INT )
BEGIN
    DECLARE done INT DEFAULT 0;
    DECLARE next_source_parent_id INT DEFAULT NULL;
    DECLARE orig_left INT DEFAULT NULL;
    DECLARE language_field VARCHAR(100);    
    DECLARE cursor1 CURSOR FOR SELECT language_id, language FROM language_family_adj_list WHERE parent_id = source_parent_id ORDER BY language;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;

    OPEN cursor1;

    read_loop: LOOP

        FETCH cursor1 INTO next_source_parent_id, language_field;

        IF done THEN
            LEAVE read_loop;
        END IF;

        SET @my_left = @my_left + 1;

        INSERT INTO language_family_mptt ( language, lft ) VALUES ( language_field, @my_left ); 

        SET orig_left = @my_left;

        CALL insert_branches( next_source_parent_id );

        UPDATE language_family_mptt SET rgt = @my_left + 1 WHERE lft = orig_left AND rgt = 0 ;

        SET @my_left = @my_left + 1;

    END LOOP;
    CLOSE cursor1;
END; ~~

DELIMITER ;

Und hier sind die Ergebnisse:

mysql> SELECT CONCAT( REPEAT( ' ', (COUNT(parent.language) - 1) ), node.language) AS name FROM language_family_mptt AS node, language_family_mptt AS parent WHERE node.lft BETWEEN parent.lft AND parent.rgt GROUP BY node.language ORDER BY node.lft;
+---------------------------------+
| name                            |
+---------------------------------+
|    Finno-Ugric                  | 
|        Baltic-Finnic            | 
|            Estonian             | 
|                South Estonian   | 
|                    Voro         | 
|            Finnish              | 
|            Ingrian              | 
|            Karelian             | 
|                Karelian Proper  | 
|                Lude             | 
|                Olonets Karelian | 
|            Livonian             | 
|            Veps                 | 
|            Votic                | 
|        Hungarian                | 
|        Khanty                   | 
|        Mansi                    | 
|        Mari                     | 
|        Mordvinic                | 
|            Erzya                | 
|            Moksha               | 
|        Permic                   | 
|            Komi                 | 
|            Komi-Permyak         | 
|            Udmurt               | 
|        Sami                     | 
|            Eastern Sami         | 
|                Akkala Sami      | 
|                Inari Sami       | 
|                Kemi Sami        | 
|                Kildin Sami      | 
|                Skolt Sami       | 
|                Ter Sami         | 
|            Western Sami         | 
|                Lule Sami        | 
|                Northern Sami    | 
|                Pite Sami        | 
|                Southern Sami    | 
|                Umi Sami         | 
+---------------------------------+
39 rows in set (0.00 sec)

:D