使用 sql 内连接从两个表中获取数据，试图获取非对象的属性

Question

I have two table events and session which looks like this

Events table

Sessions table

Here is expected results

Here is my solution

  <table>
                  <tr>
                    <th>Sessions </th>
                    <th>konto</th>
                    <th>Mobile</th>
                    <th>Komputer</th>
                    <th>Date</th>
                  </tr>       
                  <?php
                      $conn = mysqli_connect("localhost", "root", "", "ideabank_julia");
                      // Check connection
                      if ($conn->connect_error) {
                      die("Connection failed: " . $conn->connect_error);
                      }
                      $sql = "SELECT sid, datetime, count(*) as num_rows, count(distinct sid) as sessions,  
                      sum( targetbuttonname = 'konto' ) as num_konto,
                      sum(devicetype ='Computer') as num_computer, 
                      sum(devicetype = 'Mobile') as num_mobile from events
                      INNER JOIN sessions ON events.sid = sessions.sid group by sid, datetime;";

                      $result = $conn->query($sql);
                      if ($result->num_rows > 0) {
                      // output data of each row
                      while($row = $result->fetch_assoc()) {
                      echo "<tr>
                      <td>". $row["num_rows"]."</td>
                      <td>". $row["num_konto"]."</td>         
                      <td>". $row["num_mobile"]. "</td>
                      <td>". $row["num_computer"]. "</td>
                      <td>". $row["datetime"]. "</td>

                      </tr>";
                      }
                      echo "</table>";
                      } else { echo "0 results"; }
                      $conn->close();
                      ?>
                </table>

Unfortunately when i run the script on phpmyadmin I am getting the following error

 # 1052 - Column: 'sid' in field list is ambiguous

And when I run on php script above I get the following error

Trying to get property of non-object

What am I doing wrong in my code?

Answer 1

I think you should add alias to your selected columns to mention from which table you are taking the colums. Please Try the code below.

$sql = "SELECT events.sid, events.datetime, count(events.*) as num_rows, count(distinct events.sid) as sessions,  
                  sum( events.targetbuttonname = 'konto' ) as num_konto,
                  sum(events.devicetype ='Computer') as num_computer, 
                  sum(events.devicetype = 'Mobile') as num_mobile from events
                  INNER JOIN sessions ON events.sid = sessions.sid group by sid, datetime";

Answer 2

You should add alias name for coloumns in groupby condition.

  $sql = "SELECT even.sid, even.datetime, count(*) as num_rows, 
               count(distinct even.sid) as sessions,  
              sum( even.targetbuttonname = 'konto' ) as num_konto,
              sum(devicetype ='Computer') as num_computer, 
              sum(devicetype = 'Mobile') as num_mobile from events even
              INNER JOIN sessions ON even.sid = sessions.sid group by even.sid, 
              even.datetime";