Question

如何在单列中返回两个表的SQL JOIN？

例如，对于给定的组ID，如何获取属于该组的所有人员及其所有朋友的单个列表？

基

-id
-name

groups_have_people

-groups_id
-people_id

人

-id
-name
-group_id

people_have_friends

-people_id1 (references people.id)
-people_id2 (references people.id)

例如，groups_have_people包括{123}的people_id 1,2和3，而people_have_friends包括记录1-2，1-3，{{1 }}，1-4，2-1，我应该得到以下结果：

2-5

我可以执行以下操作，但它不会返回单个列表。

id Name
1  Mary
2  John
3  Burt
4  Jill
5  Sue

编辑看起来我可能不会使用JOIN来执行此操作，并且应该执行以下操作？

SELECT p1.*, p2.*
FROM people p1
INNER groups_have_people ghp ON ghp.people_id=p1.id
LEFT OUTER JOIN people_have_friends phf ON p1.id=phf.people_id1
LEFT OUTER JOIN people p2 ON p2.id=phf.people_id2
WHERE ghp.groups_id=123;

编辑2.添加更多样本数据

组

SELECT p.*
FROM people p
INNER groups_have_people ghp ON ghp.people_id=p.id
WHERE ghp.groups_id=123
UNION
SELECT people p1
INNER JOIN people_have_friends phf ON p1.id=phf.people_id1
INNER JOIN people p2 ON p2.id=phf.people_id2
WHERE p2.groups_id=123;

人

id  name
111 Green
123 Blue
222 Yello

groups_have_people

id Name
1  Mary
2  John
3  Burt
4  Jill
5  Sue
6  Bob
7  Wilma

people_have_friends

groups_id  people_id
111        1
111        5
123        1
123        2
123        3
222        3
222        7

编辑3.以下内容如何？

people_id1  people_id2
1           2
1           3
1           4
2           1
2           5
4           5
5           6

或

SELECT DISTINCT id,
                name
FROM people
WHERE id IN
    ( SELECT people_id
     FROM groups_have_people
     WHERE groups_id=123
     UNION SELECT phf.people_id
     FROM people_have_friends phf
     INNER JOIN groups_have_people ghp ON ghp.people_id=phf.people_id
     WHERE ghp.groups_id=123);

Answer 1

http://sqlfiddle.com/#!9/89a12/3

SELECT 
  p.id,
  p.name
FROM groups_have_people ghp
INNER JOIN people p 
ON ghp.people_id=p.id
WHERE ghp.groups_id=123
UNION
SELECT 
  p.id,
  p.name
FROM groups_have_people ghp
INNER JOIN people p_temp 
ON ghp.people_id=p_temp.id
INNER JOIN people_have_friends phf 
ON p_temp.id=phf.people_id1
INNER JOIN people p 
ON phf.people_id2=p.id
WHERE ghp.groups_id=123

SQL JOIN在单列

1 个答案: