MySQL在同一表中存在对应行的地方获取行

Question

我试图根据一些基本的where子句从表中获取行，现在我想在末尾添加一个“ AND EXISTS”子句。 我的代码如下：

$stmt = $mysqli->prepare("SELECT object_id FROM ".
          $db_table_prefix."user_events
          WHERE LPAD(start_timestamp,15,'0') < LPAD(?,15,'0')
          AND event_id = ?
          AND EXISTS ( 
            SELECT * FROM ".$db_table_prefix."user_events
              WHERE LPAD(start_timestamp,15,'0') > LPAD(?,15,'0')
              AND event_id = ? )
        ");

我遇到的问题是，我不知道如何从AND EXISTS子查询中的主查询中指定列值。

我正在寻找一种方法可以将此内容添加到子查询中：

AND object_id = **object_id from main query**

任何帮助表示赞赏

Answer 1

另外，为子查询的表添加别名以避免混淆

$stmt = $mysqli->prepare("SELECT object_id FROM ".
      $db_table_prefix."user_events
      WHERE LPAD(start_timestamp,15,'0') < LPAD(?,15,'0')
      AND event_id = ?
      AND EXISTS ( 
        SELECT * FROM ".$db_table_prefix."user_events AS u
          WHERE LPAD(u.start_timestamp,15,'0') > LPAD(?,15,'0')
          AND u.object_id = " .$db_table_prefix.".object_id
          AND u.event_id = ? )
    ");

Answer 2

与EXISTS相比，您可能会发现自连接语法在这里更清晰，我无法从代码中确切推断出您想要的内容，而是获取在特定时间之前启动并在以后再次启动的事件的object_id ：

SELECT  ue1.object_id 
FROM    user_events ue1 join user_events ue2
WHERE   ue1.event_id = ue2.event_id AND
        ue1.object_id = ue2.object_id AND
        ue1.event_id = ? AND 
        LPAD(ue1.start_timestamp, 15, '0') < LPAD(ue2.start_timestamp, 15, '0') AND 
        LPAD(ue1.start_timestamp, 15, '0') < LPAD(?, 15, '0')

Answer 3

和object_id in（从...中选择object_id