Question

这里我有一个标准的分层表：

CREATE TABLE GroupMembers (
   group_id    VARCHAR,
   member_id   VARCHAR
);

INSERT INTO GroupMembers VALUES
    ('1', '10'),
    ('1', '11'),
    ('10','100'),
    ('10','101'),
    ('20','200'),
    ('20','201');

现在让小组的所有成员＆＃39; 1＆＃39;我这样做：

WITH RECURSIVE members(id) AS (
   VALUES('1')
   UNION
   SELECT gm.member_id
   FROM GroupMembers gm
   INNER JOIN members m ON gm.group_id=m.id
)
SELECT * FROM members;

产生：＆＃39; 1＆＃39;，＆＃39; 10＆＃39;，＆＃39; 11＆＃39;，＆＃39; 100＆＃39;，＆＃39; 101＆＃39;

现在出现了新的皱纹：我有ids的别名

CREATE TABLE Aliases (
   member_id  VARCHAR,
   alias_id   VARCHAR
);

INSERT INTO Aliases(member_id, alias_id) VALUES
    ('11', '20');

现在我想得到所有成员。因为＆＃39; 11＆＃39;是＆＃39; 20＆＃39;的别名，结果应该是：＆＃39; 1＆＃39;，＆＃39; 10＆＃39;，＆＃39; 11＆＃39;，＆＃39; 100＆＃39;，＆＃39; 101＆＃39;，＆＃39; 200＆＃39;，＆＃39; 201＆＃39;。

我尝试了以下查询：

WITH RECURSIVE members(id) AS (
   VALUES('1')
   UNION
   SELECT gm.member_id
   FROM GroupMembers gm
   INNER JOIN members m ON gm.group_id=m.id
   UNION
   SELECT a.alias_id
   FROM Aliases
   INNER JOIN members m ON gm.group_id=m.id
)
SELECT * FROM members;

但我收到错误circular reference: members

Answer 1

这个怎么样：

WITH RECURSIVE members(id) AS (
   VALUES('1')
   UNION
   SELECT groupWithAliases.member_id
   FROM 
   ( SELECT group_id, member_id FROM GroupMembers 
     UNION
     SELECT alias_id AS group_id, member_id
     FROM Aliases ) groupWithAliases
   INNER JOIN members m ON groupWithAliases.group_id=m.id
)
SELECT * FROM members;

请注意我在构造groupWithAliases子查询时使用UNION来消除重复

你如何在递归CTE中做一个UNION？

1 个答案: