--向下查询

WITH RECURSIVE res AS (

       SELECT * FROM t_tree WHERE id = 2

     union   ALL

       SELECT t_tree.* FROM t_tree, res WHERE t_tree.pid = res.id

     )

SELECT * FROM res ORDER BY id limit 3 OFFSET (2-1)*3;--分页

--向上

WITH RECURSIVE res AS (

       SELECT * FROM t_tree WHERE id = 2

             union   ALL

       SELECT t_tree.* FROM t_tree, res WHERE t_tree.id = res.pid

       --select * from t_tree where t_tree.id = (SELECT t_tree.pid FROM t_tree WHERE id = 2) --id为id为2的记录的父id的记录，即向上查询

     )

SELECT * FROM res ORDER BY id;