递归mysql选择？

Question

我看到了this answer，我希望他是不正确的，就像有人错误地告诉主键在一个列上，而我不能在多个列上设置它。

这是我的桌子

create table Users(id INT primary key AUTO_INCREMENT,
    parent INT,
    name TEXT NOT NULL,
    FOREIGN KEY(parent)
    REFERENCES Users(id)
);


+----+--------+---------+
| id | parent | name    |
+----+--------+---------+
|  1 |   NULL | root    |
|  2 |      1 | one     |
|  3 |      1 | 1down   |
|  4 |      2 | one_a   |
|  5 |      4 | one_a_b |
+----+--------+---------+

我想选择用户 id 2 并递归，以便我得到它的所有直接和间接子项（所以 id 4 和 5）。

我如何以这样的方式编写它？我在 postgresql 和 sqlserver 中看到了递归。

Answer 1

我知道上面可能有更好和更有效的答案，但是这个 sn-p 提供了一种稍微不同的方法，并提供了 - 祖先和孩子。

这个想法是不断地将相关的rowIds插入到临时表中，然后获取一行来寻找它的亲戚，冲洗重复直到所有的行都被处理完。查询可以优化为仅使用 1 个临时表。

这是一个有效的sqlfiddle 示例。

 CREATE TABLE Users
        (`id` int, `parent` int,`name` VARCHAR(10))//
    
    INSERT INTO Users
        (`id`, `parent`, `name`)
    VALUES  
        (1, NULL, 'root'),
        (2, 1, 'one'),
        (3, 1, '1down'),
        (4, 2, 'one_a'),
        (5, 4, 'one_a_b')//
    
    CREATE PROCEDURE getAncestors (in ParRowId int) 
    BEGIN 
       DECLARE tmp_parentId int;
       CREATE TEMPORARY TABLE tmp (parentId INT NOT NULL);
       CREATE TEMPORARY TABLE results (parentId INT NOT NULL);
       INSERT INTO tmp SELECT ParRowId;
       WHILE (SELECT COUNT(*) FROM tmp) > 0 DO
         SET tmp_parentId = (SELECT MIN(parentId) FROM tmp);
         DELETE FROM tmp WHERE parentId = tmp_parentId;
         INSERT INTO results SELECT parent FROM Users WHERE id = tmp_parentId AND parent IS NOT NULL;
         INSERT INTO tmp SELECT parent FROM Users WHERE id = tmp_parentId AND parent IS NOT NULL;
       END WHILE;
       SELECT * FROM Users WHERE id IN (SELECT * FROM results);
    END//
    
    CREATE PROCEDURE getChildren (in ParRowId int) 
    BEGIN 
       DECLARE tmp_childId int;
       CREATE TEMPORARY TABLE tmp (childId INT NOT NULL);
       CREATE TEMPORARY TABLE results (childId INT NOT NULL);
       INSERT INTO tmp SELECT ParRowId;
       WHILE (SELECT COUNT(*) FROM tmp) > 0 DO
         SET tmp_childId = (SELECT MIN(childId) FROM tmp);
         DELETE FROM tmp WHERE childId = tmp_childId;
         INSERT INTO results SELECT id FROM Users WHERE parent = tmp_childId;
         INSERT INTO tmp SELECT id FROM Users WHERE parent = tmp_childId;
       END WHILE;
       SELECT * FROM Users WHERE id IN (SELECT * FROM results);
    END//

用法：

CALL getChildren(2);
                
    -- returns 
    id  parent  name
    4   2   one_a
    5   4   one_a_b


CALL getAncestors(5);
                
    -- returns 
    id  parent  name
    1   (null)  root
    2   1   one
    4   2   one_a

Answer 2

CREATE DEFINER = 'root'@'localhost'
PROCEDURE test.GetHierarchyUsers(IN StartKey INT)
BEGIN
  -- prepare a hierarchy level variable 
  SET @hierlevel := 00000;

  -- prepare a variable for total rows so we know when no more rows found
  SET @lastRowCount := 0;

  -- pre-drop temp table
  DROP TABLE IF EXISTS MyHierarchy;

  -- now, create it as the first level you want... 
  -- ie: a specific top level of all "no parent" entries
  -- or parameterize the function and ask for a specific "ID".
  -- add extra column as flag for next set of ID's to load into this.
  CREATE TABLE MyHierarchy AS
  SELECT U.ID
       , U.Parent
       , U.`name`
       , 00 AS IDHierLevel
       , 00 AS AlreadyProcessed
  FROM
    Users U
  WHERE
    U.ID = StartKey;

  -- how many rows are we starting with at this tier level
  -- START the cycle, only IF we found rows...
  SET @lastRowCount := FOUND_ROWS();

  -- we need to have a "key" for updates to be applied against, 
  -- otherwise our UPDATE statement will nag about an unsafe update command
  CREATE INDEX MyHier_Idx1 ON MyHierarchy (IDHierLevel);


  -- NOW, keep cycling through until we get no more records
  WHILE @lastRowCount > 0
  DO

    UPDATE MyHierarchy
    SET
      AlreadyProcessed = 1
    WHERE
      IDHierLevel = @hierLevel;

    -- NOW, load in all entries found from full-set NOT already processed
    INSERT INTO MyHierarchy
    SELECT DISTINCT U.ID
                  , U.Parent
                  , U.`name`
                  , @hierLevel + 1 AS IDHierLevel
                  , 0 AS AlreadyProcessed
    FROM
      MyHierarchy mh
    JOIN Users U
    ON mh.Parent = U.ID
    WHERE
      mh.IDHierLevel = @hierLevel;

    -- preserve latest count of records accounted for from above query
    -- now, how many acrual rows DID we insert from the select query
    SET @lastRowCount := ROW_COUNT();


    -- only mark the LOWER level we just joined against as processed,
    -- and NOT the new records we just inserted
    UPDATE MyHierarchy
    SET
      AlreadyProcessed = 1
    WHERE
      IDHierLevel = @hierLevel;

    -- now, update the hierarchy level
    SET @hierLevel := @hierLevel + 1;

  END WHILE;


  -- return the final set now
  SELECT *
  FROM
    MyHierarchy;

-- and we can clean-up after the query of data has been selected / returned.
--    drop table if exists MyHierarchy;


END

它可能看起来很麻烦，但是要使用它，请这样做

call GetHierarchyUsers( 5 );

（或任何您想查找 UP 层次树的键 ID）。

前提是从您正在使用的一个 KEY 开始。然后，以此为基础再次加入 users 表，但基于第一个条目的 PARENT ID。找到后，更新临时表，以免在下一个周期再次尝试加入该键。然后继续，直到找不到更多的“父”ID 密钥。

无论嵌套有多深，这都会将整个记录层次结构返回到父级。但是，如果您只想要 FINAL 父级，则可以使用 @hierlevel 变量仅返回文件中添加的最新一个，或 ORDER BY 和 LIMIT 1