插入blob文件并将其检索为PHP

I know there are hundreds of questions like this but I still can't understand how to insert and retrieve a blob.

public function uploadContent($selectIDname, $incrementVersion, $data, $getAuthorID){
        $dbManager = DatabaseConnectivityManager::getInstance();
        $connection  = $dbManager->getConnection();
        $statement = mysqli_prepare($connection, static::$insertIntoFilescontent);
        mysqli_stmt_bind_param($statement, "iisi",$selectIDname, $incrementVersion, $data, $getAuthorID);
        $uploadFilescontent = mysqli_stmt_execute($statement);
        mysqli_stmt_close($statement);
        return $uploadFilescontent;
    }

This is how i insert blobs ($data should be the blob but when in bind_param I put b nothing goes in the table, so i set it to string - s). When the user logs in he must see all his uploaded file. Here's what i've tried but it doesn't work.

    $type = $_FILES['uploadFile']['type'];
    $sql = "SELECT fileContent FROM filescontent WHERE author='$getAuthorID'";
    $query = mysqli_query($connection, $sql);
    $row = mysqli_fetch_assoc($query);
    $data = $row['fileContent'];
    header("Content-type: $type");
    print $data;