WITH
 cte1 AS (SELECT a, b FROM table1),
 cte2 AS (SELECT c, d FROM table2)
SELECT b, d FROM cte1 JOIN cte2
WHERE cte1.a = cte2.c;

WITH RECURSIVE cte_name AS
(
  SELECT ...   -- return initial row set
  UNION ALL / UNION DISTINCT
  SELECT ...   -- return additional row sets
)
SELECT * FROM cte;

WITH RECURSIVE cte (n) AS -- 这里定义的n相当于结果集的列名，也可在下面查询中定义
(
 SELECT 1
 UNION ALL
 SELECT n + 1 FROM cte WHERE n < 5
)
SELECT * FROM cte;


-- result
+------+
| n  |
+------+
|  1 |
|  2 |
|  3 |
|  4 |
|  5 |
+------+

CREATE TABLE `c_tree` (
 `id` int(11) NOT NULL AUTO_INCREMENT,
 `cname` varchar(255) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
 `parent_id` int(11) DEFAULT NULL,
 PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=13 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

mysql> select * from c_tree;
+----+---------+-----------+
| id | cname  | parent_id |
+----+---------+-----------+
| 1 | 1    |     0 |
| 2 | 2    |     0 |
| 3 | 3    |     0 |
| 4 | 1-1   |     1 |
| 5 | 1-2   |     1 |
| 6 | 2-1   |     2 |
| 7 | 2-2   |     2 |
| 8 | 3-1   |     3 |
| 9 | 3-1-1  |     8 |
| 10 | 3-1-2  |     8 |
| 11 | 3-1-1-1 |     9 |
| 12 | 3-2   |     3 |
+----+---------+-----------+

mysql> 
WITH RECURSIVE tree_cte as
(
  select * from c_tree where parent_id = 3
  UNION ALL
  select t.* from c_tree t inner join tree_cte tcte on t.parent_id = tcte.id
)
SELECT * FROM tree_cte;
+----+---------+-----------+
| id | cname  | parent_id |
+----+---------+-----------+
| 8 | 3-1   |     3 |
| 12 | 3-2   |     3 |
| 9 | 3-1-1  |     8 |
| 10 | 3-1-2  |     8 |
| 11 | 3-1-1-1 |     9 |
+----+---------+-----------+