Question

我尝试从两个不同的不相关表中选择结果showcase和questions以显示在Feed中。它们应该由公共列hotness排序，这是一个浮点值。

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

我已尝试UNION，但我不知道我应该如何在此处使用它并收到此错误unknown column hotness

Answer 1

您可以尝试此查询：

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

您需要在子查询中合并Union结果以在结果上应用Order by。我也在select子句中添加了hotness，请检查我从好的表中选择字段。

Answer 2

您需要选择值才能让ORDER BY识别它：

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;

请注意，我还将UNION更改为UNION ALL。除非您打算删除重复项，否则没有理由进行额外的处理。

加入两个按公共值排序的不同表格（热度）

2 个答案: