Mysql递归查询根级节点

SELECT T2.BUSINESS_KEY_,T2.ID_
FROM (  
    SELECT  
        @r AS id,  
        (SELECT @r := PARENT_ID_ FROM `act_ru_execution` WHERE id = ID_) AS 2v2,  
        @l := @l + 1 AS lvl  
    FROM  
        (SELECT @r := '28b0409e-edbe-11ea-9233-00ff085aa99e',@l :=0) vars,
        act_ru_execution h  
    WHERE @r is not null) T1  
left JOIN act_ru_execution T2  
ON T1.id = T2.ID_
where T2.PARENT_ID_ is null