php - Remove memory limit -

i have ms sql server , table name 'files'. table column type 'image' (or blob) there saved pdf files. , try select in php. code like

$sql = "select datalength(file) len, file files id = 1"; $stmt = $dbh->prepare($sql); $stmt->execute();  while ($row = $stmt->fetch()) {     $filelength = $row['len'];     $file = $row['file'];     break; }   echo $filelength; echo strlen($file); 

in display showed 1448484 , 64512. variable $file took 64512. file memory in database 1.4 mb. in php code variable $file takes 64kb. in fact, variable size of $file must 1.4 mb. why? how change limit? me, please. sorry english