php - 在 UNION 中选择列

Question

$queryActivities = mysql_query("
SELECT ua.status, ua.date, 'status' AS is_table FROM users_statuslog ua
   WHERE ua.uid = '{$showU[id]}'
UNION ALL 
SELECT us.message, us.date 'wall' FROM users_wall us 
   WHERE us.uid = '{$showU[id]}'
ORDER BY `date` DESC");

这就是我现在所拥有的。我需要 users_wall 中的更多列，比我在 users_statuslog 中需要的更多。我该如何选择它们？因为我不能这样做:

(假设我还想要 isReplyFrom 并从 users_wall 查看)

$queryActivities = mysql_query("
SELECT ua.status, ua.date, 'status' AS is_table FROM users_statuslog ua
   WHERE ua.uid = '{$showU[id]}'
UNION ALL 
SELECT us.message, us.date, us.isReplyFrom, us.viewed 'wall' FROM users_wall us 
   WHERE us.uid = '{$showU[id]}'
ORDER BY `date` DESC");

我得到:

使用的 SELECT 语句具有不同的列数。

Answer 1

如消息所述，您有两个列数不同的选择。
联合会将您第一次选择的结果“连接”到第二次选择，但如果列数不同，它就无法工作。

要么找到一种方法来获得相同数量的列，要么在请求中添加虚拟列:

SELECT ua.status, ua.date, 'dummy' AS replyFrom, 'dummy' AS viewed, 'status' AS is_table FROM users_statuslog ua
    WHERE ua.uid = '{$showU[id]}'
UNION ALL
SELECT us.message, us.date, us.isReplyFrom, us.viewed, 'wall' FROM users_wall us 
    WHERE us.uid = '{$showU[id]}'
ORDER BY `date` DESC

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资源:

• w3school.com - SQL UNION operator