How to keep the previous uploaded image (in db) after submitting a form without selecting a new image to be uploaded

What about something like this?

if(!empty($_FILES['fileToUpload']['name'])) //new image uploaded
{
   //process your image and data
   $sql = "UPDATE table SET name=$someName, image=$someImageName,... WHERE id = $someId";//save to DB with new image name
}
else // no image uploaded
{
   // save data, but no change the image column in MYSQL, so it will stay the same value
   $sql = "UPDATE table SET name=$someName,... WHERE id = $someId";//save to DB but no change image column
}
//process SQL query in $sql

Make a if clause that checks if fileupload input is empty or not. If it is empty do not execute query.

Use input type="file" without attribute value.

<input type="file" name="fileToUpload" id="fileToUpload" />

Here is example for if clause

if(!empty($_FILES['fileToUpload']['name'])) {
        $origFile = $_FILES['fileToUpload']['name'];
        $tempFile = $_FILES['fileToUpload']['tmp_name'];
        $sizeFile = $_FILES['fileToUpload']['size'];

        /* UPLOAD CODE GOES HERE */
    }