Большие объекты

A big gotcha exists for Oracle users.

You have to save CLOB objects using PDO::PARAM_STR, not PDO::PARAM_LOB.

But you MUST send the 4th argument, usually strlen($subject) or you get a LONG error.

PDOStatement's methods bindParam and bindValue also work with strings, as in:

<?php
  $data = file_get_contents($filename);
  $stmt->bindValue(1, $data, PDO::PARAM_LOB);
  //...
?>

This was the only way I could make it work with PostgreSQL.

There seems to be a bug that affects example 1 above. PDO::PARAM_LOB when used with pdo::bindColumn() is supposed to return a stream but it returns a string. Passing this string to fpassthru() then triggers an error with the message 'supplied argument is not a valid stream resource'. This has been reported in bug #40913. The work around is to do the following:

<?php
$stmt = $db->prepare("select contenttype, imagedata from images where id=?");
$stmt->execute(array($_GET['id']));
$stmt->bindColumn(1, $type, PDO::PARAM_STR, 256);
$stmt->bindColumn(2, $lob, PDO::PARAM_LOB);
$stmt->fetch(PDO::FETCH_BOUND);

header("Content-Type: $type");
echo($lob);
?>

Since the browser is expecting an image after the call to header() writing the string representation of the binary output with echo() has the same affect as calling fpassthru().

I spend a lot of time trying to get this to work, but no matter what I did PDO corrupted my data.

I finally discovered that I had been using:

$pdo->exec('SET CHARACTER SET utf8');

in the TRY part of my connection script.

This off course doesn't work when you feed binary input to PDO using the parameter lob.

For selecting data out of Postgres, the data type of the column in the table determined if the parameter bound with PARAM_LOB returned a string or returned a resource.

<?php

// create table log ( data text ) ;
$geth = $dbh->prepare('select data from log ');
$geth->execute();
$geth->bindColumn(1, $dataString, PDO::PARAM_LOB);
$geth->fetch(PDO::FETCH_BOUND);

echo ($dataString); // $dataString is a string

// create table log ( data bytea ) ;
$geth = $dbh->prepare('select data from log');
$geth->execute();
$geth->bindColumn(1, $dataFH, PDO::PARAM_LOB);
$geth->fetch(PDO::FETCH_BOUND);

fpassthru($dataFH); // $dataFH is a resource

The DBMSs that are listed above have these (default) limits on the maximum size of a char string. The maximum is given in bytes so the number of characters storable can be smaller if a multibyte encoding is used.

CUBRID:    16kB
SQL Server: 2GB
Firebird:  32kB
IBM Db2:   32kB
Informix:  32kB
MySQL:     16kB
Oracle:     2kB
PostgreSQL: 1GB
SQLite:     1 billion bytes
4D: Unknown, but LOBs are limited to 2GB.