再帰的なmysqlselect？

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

面倒に見えるかもしれませんが、これを使用するには

call GetHierarchyUsers( 5 );

（または、階層ツリーの上位にあるキーIDを検索します。）

前提は、作業している1つのKEYから始めることです。次に、それをベースとしてusersテーブルに再度参加しますが、最初のエントリのPARENTIDに基づいています。見つかったら、次のサイクルでそのキーに再度参加しないように一時テーブルを更新します。次に、「親」IDキーが見つからなくなるまで続行します。

これにより、ネストの深さに関係なく、レコードの階層全体が親に返されます。ただし、FINALの親のみが必要な場合は、@ hierlevel変数を使用して、追加されたファイル内の最新の親のみを返すか、ORDERBYおよびLIMIT1を返すことができます