子查询的自联接

Question

我想知道,是否有可能加入查询结果？

(我正在使用PostgreSQL)

Answer 1

您可以使用WITH:

WITH subquery AS(
    SELECT * FROM TheTable
) 
SELECT *
FROM subquery q1
JOIN subquery q2 on ...

或者通过创建包含查询的VIEW,并加入:

SELECT *
FROM TheView v1
JOIN TheView v2 on ...

或蛮力方法:键入子查询两次:

SELECT *
FROM (
    SELECT * FROM TheTable
) sub1
LEFT JOIN (
    SELECT * FROM TheTable
) sub2 ON ...