主要使用 WITH AS 关键字，如：
WITH t AS(
SELECT id,pid FROM table WHERE pid = xxx OR id = xxx
UNION ALL
SELECT c.id,c.pid FROM t p JOIN table c ON c.pid = p.id
)
SELECT * FROM t
主要使用 WITH AS 关键字，如：
WITH t AS(
SELECT id,pid FROM table WHERE pid = xxx OR id = xxx
UNION ALL
SELECT c.id,c.pid FROM t p JOIN table c ON c.pid = p.id
)
SELECT * FROM t