How to create a MySQL hierarchical recursive query

Question

I have a MySQL table which is as follows      id name parent id     19 category1 0   20 category2 19   21 category3 20   22 category4 21                   Now  I want to have a single MySQL query to which I simply supply the id  for instance say id 19  then I should get all its child ids  i e  result should have ids  20 21 22       The hierarchy of the children is not known  it can vary     I know how to do it using a for loop    but how to achieve the same using a single MySQL query

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You can do it like this in other databases quite easily with a recursive query (YMMV on performance).

The other way to do it is to store two extra bits of data, a left and right value. The left and right value are derived from a pre-order traversal of the tree structure you're representing.

This is know as Modified Preorder Tree Traversal and lets you run a simple query to get all parent values at once. It also goes by the name "nested set".

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From the blog Managing Hierarchical Data in MySQL  Table structure   ------------- ---------------------- --------    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    ------------- ---------------------- --------    Query   SELECT t1 name AS lev1  t2 name as lev2  t3 name as lev3  t4 name as lev4 FROM category AS t1 LEFT JOIN category AS t2 ON t2 parent   t1 category id LEFT JOIN category AS t3 ON t3 parent   t2 category id LEFT JOIN category AS t4 ON t4 parent   t3 category id WHERE t1 name    ELECTRONICS     Output   ------------- ---------------------- -------------- -------    lev1          lev2                   lev3           lev4     ------------- ---------------------- -------------- -------    ELECTRONICS   TELEVISIONS            TUBE           NULL      ELECTRONICS   TELEVISIONS            LCD            NULL      ELECTRONICS   TELEVISIONS            PLASMA         NULL      ELECTRONICS   PORTABLE ELECTRONICS   MP3 PLAYERS    FLASH     ELECTRONICS   PORTABLE ELECTRONICS   CD PLAYERS     NULL      ELECTRONICS   PORTABLE ELECTRONICS   2 WAY RADIOS   NULL     ------------- ---------------------- -------------- -------    Most users at one time or another have dealt with hierarchical data in a SQL database and no doubt learned that the management of hierarchical data is not what a relational database is intended for  The tables of a relational database are not hierarchical  like XML   but are simply a flat list  Hierarchical data has a parent-child relationship that is not naturally represented in a relational database table  Read more  Refer the blog for more details   EDIT   select  pv  category id as category id  name  parent from category join  select  pv  19 tmp where parent  pv   Output   category id name    parent 19  category1   0 20  category2   19 21  category3   20 22  category4   21   Reference  How to do the Recursive SELECT query in Mysql

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I found it more easily to    1  create a function that will check if a item is anywhere in the parent hierarchy of another one  Something like this  I will not write the function  make it with WHILE DO     is related id  parent id     in your example   is related 21  19     1  is related 20  19     1  is related 21  18     0    2  use a sub-select   something like this   select     from table t join table pt on pt id in  select i id from table i where is related t id i id

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Its a little tricky one  check this whether it is working for you  select a id if a parent   0  varw  concat a id       varw  concat a id      varw   as list from  select   from recursivejoin order by if parent 0 id parent  asc  a left join recursivejoin b on  a id   b parent   select  varw      as c  having list like   19       SQL fiddle link http   www sqlfiddle com   2 e3cdf 2  Replace with your field and table name appropriately

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For MySQL 8   use the recursive with syntax  For MySQL 5 x  use inline variables  path IDs  or self-joins  MySQL 8  with recursive cte  id  name  parent id  as     select     id               name               parent id   from       products   where      parent id   19   union all   select     p id               p name               p parent id   from       products p   inner join cte           on p parent id   cte id   select   from cte   The value specified in parent id   19 should be set to the id of the parent you want to select all the descendants of  MySQL 5 x For MySQL versions that do not support Common Table Expressions  up to version 5 7   you would achieve this with the following query  select  id          name          parent id  from     select   from products          order by parent id  id  products sorted           select  pv     19   initialisation where   find in set parent id   pv  and     length  pv    concat  pv       id    Here is a fiddle  Here  the value specified in  pv     19  should be set to the id of the parent you want to select all the descendants of  This will work also if a parent has multiple children  However  it is required that each record fulfills the condition parent id  lt  id  otherwise the results will not be complete  Variable assignments inside a query This query uses specific MySQL syntax  variables are assigned and modified during its execution  Some assumptions are made about the order of execution   The from clause is evaluated first  So that is where  pv gets initialised  The where clause is evaluated for each record in the order of retrieval from the from aliases  So this is where a condition is put to only include records for which the parent was already identified as being in the descendant tree  all descendants of the primary parent are progressively added to  pv   The conditions in this where clause are evaluated in order  and the evaluation is interrupted once the total outcome is certain  Therefore the second condition must be in second place  as it adds the id to the parent list  and this should only happen if the id passes the first condition  The length function is only called to make sure this condition is always true  even if the pv string would for some reason yield a falsy value   All in all  one may find these assumptions too risky to rely on  The documentation warns   you might get the results you expect  but this is not guaranteed       the order of evaluation for expressions involving user variables is undefined   So even though it works consistently with the above query  the evaluation order may still change  for instance when you add conditions or use this query as a view or sub-query in a larger query  It is a  quot feature quot  that will be removed in a future MySQL release   Previous releases of MySQL made it possible to assign a value to a user variable in statements other than SET  This functionality is supported in MySQL 8 0 for backward compatibility but is subject to removal in a future release of MySQL   As stated above  from MySQL 8 0 onward you should use the recursive with syntax  Efficiency For very large data sets this solution might get slow  as the find in set operation is not the most ideal way to find a number in a list  certainly not in a list that reaches a size in the same order of magnitude as the number of records returned  Alternative 1  with recursive  connect by More and more databases implement the SQL 1999 ISO standard WITH  RECURSIVE  syntax for recursive queries  e g  Postgres 8 4   SQL Server 2005   DB2  Oracle 11gR2   SQLite 3 8 4   Firebird 2 1   H2  HyperSQL 2 1 0   Teradata  MariaDB 10 2 2    And as of version 8 0  also MySQL supports it  See the top of this answer for the syntax to use  Some databases have an alternative  non-standard syntax for hierarchical look-ups  such as the CONNECT BY clause available on Oracle  DB2  Informix  CUBRID and other databases  MySQL version 5 7 does not offer such a feature  When your database engine provides this syntax or you can migrate to one that does  then that is certainly the best option to go for  If not  then also consider the following alternatives  Alternative 2  Path-style Identifiers Things become a lot easier if you would assign id values that contain the hierarchical information  a path  For example  in your case this could look like this      ID NAME     19 category1   19 1 category2   19 1 1 category3   19 1 1 1 category4     Then your select would look like this  select  id          name  from    products where   id like  19     Alternative 3  Repeated Self-joins If you know an upper limit for how deep your hierarchy tree can become  you can use a standard sql query like this  select      p6 parent id as parent6 id              p5 parent id as parent5 id              p4 parent id as parent4 id              p3 parent id as parent3 id              p2 parent id as parent2 id              p1 parent id as parent id              p1 id as product id              p1 name from        products p1 left join   products p2 on p2 id   p1 parent id  left join   products p3 on p3 id   p2 parent id  left join   products p4 on p4 id   p3 parent id   left join   products p5 on p5 id   p4 parent id   left join   products p6 on p6 id   p5 parent id where       19 in  p1 parent id                      p2 parent id                      p3 parent id                      p4 parent id                      p5 parent id                      p6 parent id   order       by 1  2  3  4  5  6  7   See this fiddle The where condition specifies which parent you want to retrieve the descendants of  You can extend this query with more levels as needed

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Simple query to list child s of first recursion   select  pv  id as id  name  parent id from products join  select  pv  19 tmp where parent id  pv   Result   id  name        parent id 20  category2   19 21  category3   20 22  category4   21 26  category24  22       with left join   select      pv  p1 id as id     p2 name as parent name     p1 name name     p1 parent id from products p1 join  select  pv  19 tmp left join products p2 on p2 id p1 parent id -- optional join to get parent name where p1 parent id  pv   The solution of  tincot to list all child s   select  id          name          parent id  from     select   from products          order by parent id  id  products sorted           select  pv     19   initialisation where   find in set parent id   pv   gt  0 and      pv    concat  pv       id    Test it online with Sql Fiddle and see all results   http   sqlfiddle com   9 a318e3 4 0

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Did the same thing for another quetion here  Mysql select recursive get all child with multiple level  The query will be    SELECT GROUP CONCAT lv SEPARATOR      FROM     SELECT  pv        SELECT GROUP CONCAT id SEPARATOR          FROM table WHERE parent id IN   pv      AS lv FROM table    JOIN    SELECT  pv  1 tmp   WHERE parent id IN   pv    a

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Based on the  trincot answer  very good explained  I use WITH RECURSIVE    statement to create a breadcrumb using id of the current page and go backwards in the hierarchy to find the every parent in my route table  So  the  trincot solution is adapted here in the opposite direction to find parents instead of descendants  I also added depth value which is usefull to invert result order  otherwise the breadcrumb would be upside down   WITH RECURSIVE cte        id        title        url        icon        class        parent id        depth    AS       SELECT             id            title            url            icon            class            parent id           1 AS  depth       FROM      route      WHERE     id     id            UNION ALL      SELECT          P  id           P  title           P  url           P  icon           P  class           P  parent id            depth    1     FROM  route  P              INNER JOIN cte         ON P  id    cte  parent id    SELECT   FROM cte ORDER BY  depth  DESC    Before upgrade to mySQL 8   I was using vars but it s deprecated and no more working on my 8 0 22 version    EDIT 2021-02-19   Example for hierarchical menu After  david comment I decided to try to make a full hierarchical menu with all nodes and sorted as I want  with sorting column which sort items in each depth   Very usefull for my user authorization matrix page  This really simplifies my old version with one query on each depth  PHP loops    This example intergrates an INNER JOIN with url table to filter route by website  multi-websites CMS system   You can see the essential path column that contains CONCAT   function to sort the menu in the right way  SELECT R   FROM       WITH RECURSIVE cte            id            title            url            icon            class            parent            depth            sorting            path        AS           SELECT               id                title                url                icon                class                parent               1 AS  depth                sorting               CONCAT  sorting          title   AS  path          FROM  route          WHERE  parent    0         UNION ALL SELECT              D  id               D  title               D  url               D  icon               D  class               D  parent                depth    1              D  sorting               CONCAT cte  path      gt     D  sorting         D  title           FROM  route  D         INNER JOIN cte             ON cte  id    D  parent            SELECT   FROM cte   R  INNER JOIN  url  U     ON R  id    U  route id      AND U  site id    1  ORDER BY  path  ASC

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If you need quick read speed  the best option is to use a closure table  A closure table contains a row for each ancestor descendant pair  So in your example  the closure table would look like  ancestor   descendant   depth 0          0            0 0          19           1 0          20           2 0          21           3 0          22           4 19         19           0 19         20           1 19         21           3 19         22           4 20         20           0 20         21           1 20         22           2 21         21           0 21         22           1 22         22           0   Once you have this table  hierarchical queries become very easy and fast  To get all the descendants of category 20   SELECT cat   FROM categories closure AS cl INNER JOIN categories AS cat ON cat id   cl descendant WHERE cl ancestor   20 AND cl depth  gt  0   Of course  there is a big downside whenever you use denormalized data like this  You need to maintain the closure table alongside your categories table  The best way is probably to use triggers  but it is somewhat complex to correctly track inserts updates deletes for closure tables  As with anything  you need to look at your requirements and decide what approach is best for you   Edit  See the question What are the options for storing hierarchical data in a relational database  for more options  There are different optimal solutions for different situations

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It s a category table   SELECT  id          NAME          parent category  FROM     SELECT   FROM category          ORDER BY parent category  id  products sorted           SELECT  pv     2   initialisation WHERE   FIND IN SET parent category   pv   gt  0 AND      pv    CONCAT  pv       id    Output

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This works for me  hope this will work for you too  It will give you a Record set Root to Child for any Specific Menu  Change the Field name as per your requirements   SET  id    22    SELECT Menu Name    id  Sub Menu ID   as Sub Menu ID  Menu ID  FROM        SELECT Menu ID  Menu Name  Sub Menu ID        FROM menu        ORDER BY Sub Menu ID DESC       AS aux table      WHERE Menu ID    id      ORDER BY Sub Menu ID

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I have made a query for you  This will give you Recursive Category with a Single Query   SELECT id NAME    AS subName    AS subsubName    AS subsubsubName FROM Table1 WHERE prent is NULL UNION  SELECT b id a name b name AS subName    AS subsubName    AS subsubsubName FROM Table1 AS a LEFT JOIN Table1 AS b ON b prent a id WHERE a prent is NULL AND b name IS NOT NULL  UNION  SELECT c id a name b name AS subName c name AS subsubName    AS subsubsubName FROM Table1 AS a LEFT JOIN Table1 AS b ON b prent a id LEFT JOIN Table1 AS c ON c prent b id WHERE a prent is NULL AND c name IS NOT NULL  UNION  SELECT d id a name b name AS subName c name AS subsubName d name AS subsubsubName FROM Table1 AS a LEFT JOIN Table1 AS b ON b prent a id LEFT JOIN Table1 AS c ON c prent b id LEFT JOIN Table1 AS d ON d prent c id WHERE a prent is NULL AND d name IS NOT NULL  ORDER BY NAME subName subsubName subsubsubName   Here is a fiddle

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The best approach I ve come up with is   Use lineage to store sort trace trees  That s more than enough  and works thousands times faster for reading than any other approach  It also allows to stay on that pattern even if DB will change as ANY db will allow that pattern to be used  Use function that determines lineage for specific ID  Use it as you wish  in selects  or on CUD operations  or even by jobs     Lineage approach descr  can be found wherever  for example Here or here  As of function - that is what enspired me   In the end - got more-or-less simple  relatively fast  and SIMPLE solution   Function s body  -- -------------------------------------------------------------------------------- -- Routine DDL -- Note  comments before and after the routine body will not be stored by the server -- -------------------------------------------------------------------------------- DELIMITER     CREATE DEFINER  root   localhost  FUNCTION  get lineage  the id INT  RETURNS text CHARSET utf8     READS SQL DATA BEGIN   DECLARE v rec INT DEFAULT 0    DECLARE done INT DEFAULT FALSE   DECLARE v res text DEFAULT      DECLARE v papa int   DECLARE v papa papa int DEFAULT -1   DECLARE csr CURSOR FOR    select  id parent id --  n   n 1 as rownum T1      from       SELECT  r AS  id           SELECT  r    table parent id FROM table WHERE table id    id  AS parent id           l     l   1 AS lvl     FROM          SELECT  r    the id   l    0  n  0  vars          table m     WHERE  r  lt  gt  0       T1     where T1 parent id is not null  ORDER BY T1 lvl DESC   DECLARE CONTINUE HANDLER FOR NOT FOUND SET done   TRUE      open csr      read loop  LOOP     fetch csr into v papa v papa papa          SET v rec   v rec 1          IF done THEN             LEAVE read loop          END IF          -- add first         IF v rec   1 THEN             SET v res   v papa papa          END IF          SET v res   CONCAT v res  -  v papa       END LOOP      close csr      return v res  END   And then you just  select get lineage the id    Hope it helps somebody

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Just use BlueM tree php class for make tree of a self-relation table in mysql      Tree  and  Tree Node  are PHP classes for handling data that is structured hierarchically using parent ID references  A typical example is a table in a relational database where each record   s    parent    field references the primary key of another record  Of course  Tree cannot only use data originating from a database  but anything  you supply the data  and Tree uses it  regardless of where the data came from and how it was processed  read more   Here is an example of using BlueM tree    lt  php  require   path to vendor autoload php    db   new PDO          Set up your database connection   stm    db- gt query  SELECT id  parent  title FROM tablename ORDER BY title      records    stm- gt fetchAll PDO  FETCH ASSOC     tree   new BlueM Tree  records

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Something not mentioned here  although a bit similar to the second alternative of the accepted answer but different and low cost for big hierarchy query and easy  insert update delete  items  would be  adding a persistent path  column for each item   some like   id   name          path 19   category1      19 20   category2      19 20 21   category3      19 20 21 22   category4      19 20 21 22   Example   -- get children of category3  SELECT   FROM my table WHERE path LIKE   19 20 21   -- Reparent an item  UPDATE my table SET path   REPLACE path    19 20     15 16   WHERE path LIKE   19 20      Optimise the path length and ORDER BY path using base36 encoding instead real numeric path id       base10   gt  base36   1    gt   1     10    gt   A     100    gt   2S     1000    gt   RS     10000    gt   7PS     100000    gt   255S     1000000    gt   LFLS     1000000000    gt   GJDGXS     1000000000000    gt   CRE66I9S    https   en wikipedia org wiki Base36  Suppressing also the slash     separator by using fixed length and padding to the encoded id  Detailed optimization explanation here  https   bojanz wordpress com 2014 04 25 storing-hierarchical-data-materialized-path   TODO  building a function or procedure to split path for retreive ancestors of one item

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Try these   Table definition   DROP TABLE IF EXISTS category  CREATE TABLE category       id INT AUTO INCREMENT PRIMARY KEY      name VARCHAR 20       parent id INT      CONSTRAINT fk category parent FOREIGN KEY  parent id      REFERENCES category  id    engine innodb    Experimental rows   INSERT INTO category VALUES  19   category1   NULL    20   category2   19    21   category3   20    22   category4   21    23   categoryA   19    24   categoryB   23    25   categoryC   23    26   categoryD   24     Recursive Stored procedure   DROP PROCEDURE IF EXISTS getpath  DELIMITER    CREATE PROCEDURE getpath IN cat id INT  OUT path TEXT  BEGIN     DECLARE catname VARCHAR 20       DECLARE temppath TEXT      DECLARE tempparent INT      SET max sp recursion depth   255      SELECT name  parent id FROM category WHERE id cat id INTO catname  tempparent      IF tempparent IS NULL     THEN         SET path   catname      ELSE         CALL getpath tempparent  temppath           SET path   CONCAT temppath       catname       END IF  END   DELIMITER     Wrapper function for the stored procedure   DROP FUNCTION IF EXISTS getpath  DELIMITER    CREATE FUNCTION getpath cat id INT  RETURNS TEXT DETERMINISTIC BEGIN     DECLARE res TEXT      CALL getpath cat id  res       RETURN res  END   DELIMITER     Select example   SELECT id  name  getpath id  AS path FROM category    Output    ---- ----------- -----------------------------------------    id   name        path                                       ---- ----------- -----------------------------------------    19   category1   category1                                   20   category2   category1 category2                         21   category3   category1 category2 category3               22   category4   category1 category2 category3 category4     23   categoryA   category1 categoryA                         24   categoryB   category1 categoryA categoryB               25   categoryC   category1 categoryA categoryC               26   categoryD   category1 categoryA categoryB categoryD    ---- ----------- -----------------------------------------    Filtering rows with certain path   SELECT id  name  getpath id  AS path FROM category HAVING path LIKE  category1 category2      Output    ---- ----------- -----------------------------------------    id   name        path                                       ---- ----------- -----------------------------------------    20   category2   category1 category2                         21   category3   category1 category2 category3               22   category4   category1 category2 category3 category4    ---- ----------- -----------------------------------------

[mysql] How to create a MySQL hierarchical recursive query?

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