SQL：2列1的結果集

info_contact：

id_contact  id_demand  email 
    1    1  [email protected] 
    2    2  [email protected] 
    3    3  [email protected]

需求：

id_demand date 
    1  2016-10-12  
    2  2016-11-05  
    3  2016-12-12

邀請：

id_invitation id_demand partner_company concurrent_company 
    1    1    google   facebook 
    2    1    null   linkedin 
    3    2    google    null 
    4    2    null    yahoo 
    5    3    google    null

我想有那樣的結果：

 Company | id_demand 
    ---------------------- 
    Facebook |  1 
    Google |  1 
    Google |  2 
    Google |  3 
    Linkedin |  1 
    Yahoo |  2

與（在一起的結果）partner_company和concurrent_company之間沒有什麼區別。

因爲我已經嘗試了一下：

SELECT i.partner_company, d.id_demand 
FROM info_contact as c, demand as d, invitation as i 
WHERE c.id_demand = d.id_demand AND d.id_demand = i.id_demand 
AND i.partner_company IS NOT NULL 
GROUP BY i.partner_company, d.id_demand;

和

SELECT i.concurrent_company, d.id_demand 
FROM info_contact as c, demand as d, invitation as i 
WHERE c.id_demand = d.id_demand AND d.id_demand = i.id_demand 
AND i.concurrent_company IS NOT NULL 
GROUP BY i.concurrent_company, d.id_demand;

，我不知道如何將這些2個查詢相結合，獲得的結果，我想

來源

2016-10-23 isy

嘗試使用UNION ALL

select partner_company , id_demand 
From invitation 
Where partner_company is not null 
Union All 
select concurrent_company , id_demand 
From invitation 
Where concurrent_company is not null

另外我沒有JOIN其他表，因爲你沒有選擇他們。如果你想檢查存在，那麼JOIN它。使用INNER JOIN語法加入表

來源

2016-10-23 17:11:15

Thx，它工作:) – isy

SQL：2列1的結果集

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