显示union select语句的结果时出错

Question

The following query works, but for some reason the first select statement is the only URL being displayed. Items from other tables are displayed, however, their URL is wrong.

$sql = "(SELECT postsID as postsID, postsSubject AS postsSubject, postsTimestamp AS timestamp
                FROM   posts
                WHERE  postsCategory = '$id')
            UNION 
                (SELECT eventID as eventID, eventTitle as eventTitle, eventsTimestamp as timestamp
                FROM   events
                WHERE  eventLocation = '$id')
            ORDER BY timestamp DESC";

The information is being correctly displayed from both the events and posts table, but the results are appearing to ONLY come from the posts table.

For example, say I have the following info

postsID |  postsSubject |  postsTimestamp
  1            post             123

eventID |  eventTitle   | eventsTimestamp
  2           event            456

I have the following to display my results

   while($row = mysql_fetch_assoc($result)){
    ?>
        <tr><td><? echo '<a href="viewevent.php?eventID=' . $row['eventID'] . '">' . $row['eventTitle'] . '</a>' ; ?></td>
        <tr><td><? echo '<a href="viewpost.php?postID=' . $row['postsID'] . '">' . $row['postsSubject'] . '</a>' ; ?></td>
    <?  
        if(preg_match('/[0-9]/',$row['timestamp'])){        
            list($yyyy,$dd,$mm) = explode('-',$row['timestamp']);
                    $newDate = $dd."-".$mm."-".$yyyy;
            }
        ?>
            <td><center><? echo $newDate; ?></center></td></tr>
        <?
        }
        echo '</table>';
}

The output appears to be correct

post   123
event  456

However, both results link to the following (respectively)

viewpost.php?id = 1
viewpost.php?id = 2  //this should be viewevent.php

Answer 1

sql as below:

$sql = "(SELECT postsID as ids, postsSubject AS description, postsTimestamp AS timestamp,'p' as status
                FROM   posts
                WHERE  postsCategory = '$id')
            UNION 
                (SELECT eventID as ids, eventTitle as description, eventsTimestamp as timestamp, 'e' as status
                FROM   events
                WHERE  eventLocation = '$id')
            ORDER BY timestamp DESC";

when retrieving data,

while($row = mysql_fetch_assoc($result)){
     if ($row['status']=="e"){
    ?>
        <tr><td><? echo '<a href="viewevent.php?eventID=' . $row['ids'] . '">' . $row['description'] . '</a>' ; ?></td>
<? }else{?>
        <tr><td><? echo '<a href="viewpost.php?postID=' . $row['ids'] . '">' . $row['description'] . '</a>' ; ?></td>
<? } ?>
    <?  
        if(preg_match('/[0-9]/',$row['timestamp'])){        
            list($yyyy,$dd,$mm) = explode('-',$row['timestamp']);
                    $newDate = $dd."-".$mm."-".$yyyy;
            }
        ?>
            <td><center><? echo $newDate; ?></center></td></tr>
        <?
        }
        echo '</table>';
}

Answer 2

A union/union all brings the rows together in one table, using the columns from the first table. So, the result set has a PostsId, but no EventsId.

Perhaps you want a join, which will put the columns side-by-side. Perhaps you want to run this as two separate queries.

Here is the example:

$sql = "select *
        from (SELECT postsID as postsID, postsSubject AS postsSubject, postsTimestamp AS timestamp
                FROM   posts
                WHERE  postsCategory = '$id') p
            cross join
                (SELECT eventID as eventID, eventTitle as eventTitle, eventsTimestamp as timestamp
                FROM   events
                WHERE  eventLocation = '$id') e
            ORDER BY postsTimeStamp DESC"

Do note that this is producing a cartesian product. So, if there are more rows from one of the tables, then you will get a proliferation of rows.