Selecting fields using variable PHP - php

Question

how can I select the field using variable. I want to select the field (Seriennummer) in the base column (Seriennummer, MacAdresse).
I need to select meta_key columns, and meta_value where the variable $result is equal to meta_key.
Thanks to everyone for help.
I always get an error
Catchable fatal error: Object of class stdClass could not be converted to string in \wp-content\plugins\woocommerce\templates\checkout\thankyou.php
$result = wpuef_get_field('c2');
$value=$result->value;
echo $value,"<br>";
//Sql
$link = mysqli_connect("localhost", "root", "", "paymentdb");
// Check connection
if($link === false){
die("ERROR: Could not connect. " . mysqli_connect_error());
}
// Attempt select query execution
$sql = "SELECT Seriennummer, MacAdresse FROM set_top_box WHERE Seriennummer ='".$result."'";
if($result = mysqli_query($link, $sql)){
if(mysqli_num_rows($result) > 0){
echo "<table>";
echo "<tr>";
echo "<th>Seriennummer</th>";
echo "<th>MacAdresse</th>";
echo "</tr>";
while($row = mysqli_fetch_array($result)){
echo "<tr>";
echo "<td>" . $row['Seriennummer'] . "</td>";
echo "<td>" . $row['MacAdresse'] . "</td>";
echo "</tr>";
}
echo "</table>";
// Free result set
mysqli_free_result($result);
} else{
echo "No records matching your query were found.";
}
} else{
echo "ERROR: Could not able to execute $sql. " . mysqli_error($link);
}
// Close connection
mysqli_close($link);
database picture

Answer 1

this is the result
$result = wpuef_get_field('c2');
$value=$result->value;
echo $value,"<br>";
//Sql
$link = mysqli_connect("localhost", "root", "", "paymentdb");
// Check connection
if($link === false){
die("ERROR: Could not connect. " . mysqli_connect_error());
}
// Attempt select query execution
$sql = "SELECT Seriennummer, MacAdresse FROM set_top_box WHERE Seriennummer ='".$value=$result->value."'";
if($result = mysqli_query($link, $sql)){
if(mysqli_num_rows($result) > 0){
echo "<table>";
echo "<tr>";
echo "<th>Seriennummer</th>";
echo "<th>MacAdresse</th>";
echo "</tr>";
while($row = mysqli_fetch_array($result)){
echo "<tr>";
echo "<td>" . $row['Seriennummer'] . "</td>";
echo "<td>" . $row['MacAdresse'] . "</td>";
echo "</tr>";
}
echo "</table>";
// Free result set
mysqli_free_result($result);
} else{
echo "No records matching your query were found.";
}
} else{
echo "ERROR: Could not able to execute $sql. " . mysqli_error($link);