Question

我有两个mysql表如下：

联系人

---------------
id | name | email
---------------
1  | Jack | jack@test.com
2  | John | john@test.com
3  | Liz  | liz@test.com
5  | Jack | jack@test.com
6  | Liz  | liz@test.com
7  | Mike | mike@test.com
8  | Jack | jack@test.com

购买

-------------------
id | contact_id | paid
-------------------
1  | 3          | true
2  | 5          | true

我需要使用独特的contact_ids来购买和购买其他独特的contact_ids。

所以最终的结果将是：

-------------------
id | name | email
------------------
2  | John | john@test.com
3  | Liz  | liz@test.com
5  | Jack | jack@test.com
7  | Mike | mike@test.com

我尝试了查询：

SELECT * FROM contacts LEFT JOIN purchases ON contacts.id = purchases.user_id

但这并没有按要求给我独特的行。我尝试了几种DISTINCT组合，但我没有按要求得到结果。

Answer 1

你试过这个吗？

SELECT COALESCE(purchases.contact_id, contacts.id) as id, name, email
FROM contacts 
LEFT JOIN purchases ON contacts.id = purchases.user_id
GROUP BY name

SQL FIDDLE

Answer 2

这样的东西应该有效，但它的表现是“？”。

SELECT * FROM contacts WHERE id IN (
    SELECT DISTINCT id as i FROM purchases
    UNION
    SELECT DISTINCT contact_id as i FROM purchases
    )
GROUP BY id

具有条件的表中的Mysql数据

2 个答案: