Question

我遇到查询问题，应该得到喜欢和回复，它有相同类型的字段，所以我可以通过1个查询来阅读它们，这对我的客户端应用程序来说是最好的..有没有人知道如何添加像第一个选择语句的字段，如thisisareply =＆＃39; x＆＃39;第二个是thisisareply =＆＃39;＆＃39;

这是我目前所拥有的：

SELECT 
        a.alerts,a.title,r.id as replyid, r.date_added as replydatum,
        u.id as user_id,u.username,u.profile_picture 
    FROM 
        `alerts` a
    LEFT JOIN 
        `reply` r 
        ON 
            a.alerts = r.alert_id 
    LEFT JOIN 
        `users` u 
        ON 
            u.id = r.user_id 
    WHERE 
        a.user_id = '2' 
    GROUP BY 
        replyid 

UNION 

SELECT 
        a.alerts,a.title,i.id as interactionid, i.date_added as likedatum
        ,u.id as user_id,u.username,u.profile_picture 
    FROM 
        `alerts` a 
    LEFT JOIN 
        `interactions` i 
        ON 
            a.alerts = i.alert_id 
    LEFT JOIN 
        `users` u 
        ON 
            u.id = i.user_id 
    WHERE 
        a.user_id = '2' 
    GROUP BY 
        likedatum

Answer 1

是的，您可以使用'x'和null

定义别名thisisareply

SELECT 
        a.alerts,a.title,r.id as replyid, r.date_added as replydatum,
        u.id as user_id,u.username,u.profile_picture , 'x' AS thisisareply 
    FROM ....
UNION 
SELECT 
        a.alerts,a.title,i.id as interactionid, i.date_added as likedatum
        ,u.id as user_id,u.username,u.profile_picture, null as thisisareply 
    FROM ...

Answer 2

尝试这样的事情：

SELECT 'something' as ReplyType,
    a.alerts,a.title,r.id as replyid, r.date_added as replydatum,
    u.id as user_id,u.username,u.profile_picture 
FROM 
    `alerts` a
LEFT JOIN 
    `reply` r 
    ON 
        a.alerts = r.alert_id 
LEFT JOIN 
    `users` u 
    ON 
        u.id = r.user_id 
WHERE 
    a.user_id = '2' 
GROUP BY 
    replyid 

UNION 

SELECT 'something else' as ReplyType,
    a.alerts,a.title,i.id as interactionid, i.date_added as likedatum
    ,u.id as user_id,u.username,u.profile_picture 
FROM 
    `alerts` a 
LEFT JOIN 
    `interactions` i 
    ON 
        a.alerts = i.alert_id 
LEFT JOIN 
    `users` u 
    ON 
        u.id = i.user_id 
WHERE 
    a.user_id = '2' 
GROUP BY 
    likedatum

选择带有联合和联接的语句，并添加一个不同的字段来定义行类型

2 个答案: