Php-sql result in joomla displayed in question marks

Question

I have a simple sql query, in a joomla php server, rs forms pro. The result contains Greek characters. However, the result is displayed in question marks.

$sql = "SELECT `FieldValue` FROM `table` where `FieldName` = 'age' and `SubmissionId` =   ".$submissionId."
";


$result = $conn->query($sql);

if ($result->num_rows > 0) {
    // output data of each row
    while($row = $result->fetch_assoc()) 

{ echo
     $row["FieldValue"] ; 
}

Result:

??? 20 ???? (question marks should be Greek letters)

I tried using convert as utf8, and it did not work. Likewise with

 header('Content-type: text/plain; charset=utf-8');
header('Content-Type: charset=utf-8');
mysqli_set_charset($con, 'utf8mb4');

They did not work either. What else can i do?

 $sql = "SELECT CONVERT(`FieldValue` USING utf8) as `FieldValue`
  FROM `table` where `FieldName` = 'age' and `SubmissionId` =   ".$submissionId."";

Answer 1

Try doing below stuff if you are using mysql:

after you connect to the mysql, do this query to make sure that you are using UTF8:

mysql_query("SET NAMES 'utf8'");
mysql_query("SET CHARACTER SET 'utf8'");

Also make sure you are using right encoding in your html head

<meta http-equiv="content-type" content="text/html; charset=UTF-8">

If this does not work you can try different character sets for the same. This link might help you, Also one suggestion Use Joomla's methods for query building.