連接兩個不同的表，按公用值（熱度）排序

Question

我正在嘗試從兩個不相關的表格， showcase和questions要顯示在供稿中的結果。 它們應按公共列hotness （浮點值）排序。

SELECT s.id,s.date,s.title,s.views,s.image,s.hidpi,s.width,s.description,u.display_name,u.avatar
FROM showcase AS s
INNER JOIN users AS u ON s.user_id = u.id
UNION 
SELECT q.id,q.date,q.title,q.views,q.text,u.display_name,u.avatar,0,0,0
FROM questions AS q
INNER JOIN users AS u ON q.user_id = u.id
ORDER BY hotness DESC
LIMIT 10

我已經嘗試了UNION ，但是我不知道我應該如何在這里使用它並得到此錯誤unknown column hotness

Answer 1

您可以嘗試以下查詢：

SELECT r.* FROM (
    SELECT s.id,s.date,s.title,s.views,s.image,s.hidpi,s.width,s.description,u.display_name,u.avatar, s.hotness
    FROM showcase AS s
    INNER JOIN users AS u ON s.user_id = u.id
    UNION 
    SELECT q.id,q.date,q.title,q.views,q.text,u.display_name,u.avatar,0,0,0, q.hotness
    FROM questions AS q
    INNER JOIN users AS u ON q.user_id = u.id 
) as r
ORDER BY r.hotness DESC
LIMIT 10

您需要在子查詢中合並聯合結果以對結果應用Order by。 我還在select子句中添加了熱點，請檢查我從好表中獲取字段。

Answer 2

您需要選擇值，以便ORDER BY可以識別它：

SELECT s.id,s.date,s.title,s.views,s.image,s.hidpi,s.width,s.description,u.display_name,u.avatar, s.hotness
FROM showcase AS s
INNER JOIN users AS u ON s.user_id = u.id
UNION ALL
SELECT q.id,q.date,q.title,q.views,q.text,u.display_name,u.avatar,0,0,0, q.hotness
FROM questions AS q
INNER JOIN users AS u ON q.user_id = u.id
ORDER BY hotness DESC;

請注意，我還將UNION更改為UNION ALL 。 除非您打算刪除重復項，否則沒有理由進行額外的處理。