LEFT JOIN on PHP - php

Question

I have tried the same code below on my c# app and it works fine, but when i tried the same code on php with the tweak of instead of column number on c# i replaced it with column name but the result is different.
$sql ="SELECT
`adexposure`.`symbol`,
`adexposure`.`netvolume`,
`fxexposure`.`netvolume`,
`adexposure`.`lastupdate`
FROM `adexposure`
LEFT JOIN `fxexposure` ON `adexposure`.`symbol` = `fxexposure`.`symbol`";
$result = $conn->query($sql);
if($result->num_rows>0)
{
echo "<table>";
echo "<tr>";
echo "<th>Symbol</th>";
echo "<th>Net Volume A</th>";
echo "<th>Net Volume B</th>";
echo "<th>Last Update</th>";
echo "</tr>";
while($row = $result->fetch_assoc())
{
echo "<tr>";
echo "<td>" .$row["symbol"]."</td>";
echo "<td>" .$row["netvolume"]."</td>";
echo "<td>" .$row["netvolume"]."</td>";
echo "<td>" .$row["lastupdate"]."</td>";
echo "</tr>";
}
echo "</table>";
}
else
{
echo "0 results";
}
Result should be:
<table border=1>
<tr>
<th>Symbol</th>
<th>Net Volume A</th>
<th>Net Volume B</th>
<th>Last Update</th>
</th>
</tr>
<tr>
<td>BITCOIN</td>
<td>2.5</td>
<td>3.5</td>
<td>2018.02.05 10:44</td>
</tr>
<tr>
<td>LITECOIN</td>
<td>1.5</td>
<td>5.5</td>
<td>2018.02.05 10:44</td>
</tr>
<tr>
<td>HASHCOIN</td>
<td>0.5</td>
<td>0.5</td>
<td>2018.02.05 10:44</td>
</tr>
</table>
but thats not the case.
The result shows both net volume of fxexposure.netvolume.
I hope you can help me with this.
Thanks...

Answer 1

just a suggestion you have two time netvolumn so you should use alias
sql ="SELECT
`adexposure`.`symbol`,
`adexposure`.`netvolume`,
`fxexposure`.`netvolume` as netvolume2,
`adexposure`.`lastupdate`
FROM `adexposure`
LEFT JOIN `fxexposure` ON `adexposure`.`symbol` = `fxexposure`.`symbol`";
while($row = $result->fetch_assoc())
{
echo "<tr>";
echo "<td>" .$row["symbol"]."</td>";
echo "<td>" .$row["netvolume"]."</td>";
echo "<td>" .$row["netvolume2"]."</td>";
echo "<td>" .$row["lastupdate"]."</td>";
echo "</tr>";
}

Answer 2

If you assign an alias to the returned colums you can address them correctly in the php
$sql ="SELECT
`adexposure`.`symbol`,
`adexposure`.`netvolume` as `netvolume_A`, /* ALIAS */
`fxexposure`.`netvolume` as `netvolume_B`,
`adexposure`.`lastupdate`
FROM `adexposure`
LEFT JOIN `fxexposure` ON `adexposure`.`symbol` = `fxexposure`.`symbol`";
$result = $conn->query($sql);
if($result->num_rows>0)
{
echo "<table>";
echo "<tr>";
echo "<th>Symbol</th>";
echo "<th>Net Volume A</th>";
echo "<th>Net Volume B</th>";
echo "<th>Last Update</th>";
echo "</tr>";
while($row = $result->fetch_assoc())
{
echo "<tr>";
echo "<td>" .$row["symbol"]."</td>";
echo "<td>" .$row["netvolume_A"]."</td>";<!-- /* ALIAS */ -->
echo "<td>" .$row["netvolume_B"]."</td>";
echo "<td>" .$row["lastupdate"]."</td>";
echo "</tr>";
}
echo "</table>";
}
else
{
echo "0 results";
}

Answer 3

Read these two lines carefully:
echo "<td>" .$row["netvolume"]."</td>";
echo "<td>" .$row["netvolume"]."</td>";
You are using the same name to mean two different things, so there is no way for PHP to give a different result on those lines.
The solution is to give the values unique column aliases in your SQL:
`adexposure`.`netvolume` as netvolume_as,
`fxexposure`.`netvolume` as netvolume_fx,
And then those are the names in your PHP:
echo "<td>" .$row["netvolume_as"]."</td>";
echo "<td>" .$row["netvolume_fx"]."</td>";