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Using PHP to upload files into MySQL database sometimes needed by
some web application. For instance for storing pdf documents or images
to make som kind of online briefcase (like Yahoo briefcase).

For the first step, let's make the table for the upload files. The table will consist of.

1. id : Unique id for each file
2. name : File name
3. type : File content type
4. size : File size
5. content : The file itself

For column content we'll use BLOB data type. BLOB is a binary large
object that can hold a variable amount of data. MySQL have four BLOB
data types, they are :

* TINYBLOB
* BLOB
* MEDIUMBLOB
* LONGBLOB

Since BLOB is limited to store up to 64 kilobytes of data we will
use MEDIUMBLOB so we can store larger files ( up to 16 megabytes ).

Example : upload.txt
CREATE TABLE upload (
id INT NOT NULL AUTO_INCREMENT,
name VARCHAR(30) NOT NULL,
type VARCHAR(30) NOT NULL,
size INT NOT NULL,
content MEDIUMBLOB NOT NULL,
PRIMARY KEY(id)
);

Uploading a file to MySQL is a two step process. First you need to
upload the file to the server then read the file and insert it to MySQL.

For uploading a file we need a form for the user to enter the file
name or browse their computer and select a file. The input type="file"
is used for that purpose.

Example : upload.php
Source code : upload.phps

see attached file

An upload form must have encytype="multipart/form-data" otherwise it
won't work at all. Of course the form method also need to be set to
method="post". Also remember to put a hidden input MAX_FILE_SIZE before
the file input. It's to restrict the size of files.

After the form is submitted the we need to read the autoglobal
$_FILES. In the example above the input name for the file is userfile
so the content of $_FILES are like this :

$_FILES['userfile']['name']
The original name of the file on the client machine.

$_FILES['userfile']['type']
The mime type of the file, if the browser provided this information. An example would be "image/gif".

$_FILES['userfile']['size']
The size, in bytes, of the uploaded file.

$_FILES['userfile']['tmp_name']
The temporary filename of the file in which the uploaded file was stored on the server.

$_FILES['userfile']['error']
The error code associated with this file upload. ['error'] was added in PHP 4.2.0

Example : upload.php
Source code : upload.phps

see attached file

Before you do anything with the uploaded file. You should not assume
that the file was uploaded successfully to the server. Always check to
see if the file was successfully uploaded by looking at the file size.
If it's larger than zero byte then we can assume that the file is
uploaded successfully.

PHP saves the uploaded file with a temporary name and save the name
in $_FILES['userfile']['tmp_name']. Our next job is to read the content
of this file and insert the content to database. Always make sure that
you use addslashes() to escape the content. Using addslashes() to the
file name is also recommended because you never know what the file name
would be.

That's it now you can upload your files to MySQL. Now it's time to write the script to download those files.

Downloading Files From MySQL Database

When we upload a file to database we also save the file type and
length. These were not needed for uploading the files but is needed for
downloading the files from the database.

The download page list the file names stored in database. The names
are printed as a url. The url would look like download.php?id=3. To see
a working example click here. I saved several images in my database,
you can try downloading them.

Example : download.php
Source code : download.phps

see attached file

When you click the download link, the $_GET['id'] will be set. We
can use this id to identify which files to get from the database. Below
is the code for downloading files from MySQL Database.

Example : download.php
Source code : download.phps

see attached file

Before sending the file content using echo first we need to set several headers. They are :

1. header("Content-length: $size")
This header tells the
browser how large the file is. Some browser need it to be able to
download the file properly. Anyway it's a good manner telling how big
the file is. That way anyone who download the file can predict how long
the download will take.
2. header("Content-type: $type")
This header tells the browser what kind of file it tries to download.
3. header("Content-Disposition: attachment; filename=$name");
Tells the browser to save this downloaded file under the specified
name. If you don't send this header the browser will try to save the
file using the script's name (download.php).

After sending the file the script stops executing by calling exit.

NOTE :
When sending headers the most common error message you will see is something like this :

Warning: Cannot modify header information - headers already sent by
(output started at C:\Webroot\library\config.php:7) in
C:\Webroot\download.php on line 13

This error happens because some data was already sent before we send
the header. As for the error message above it happens because i
"accidentally" add one space right after the PHP closing tag ( ?> )
in config.php file. So if you see this error message when you're
sending a header just make sure you don't have any data sent before
calling header(). Check the file mentioned in the error message and go
to the line number specified

All the files required for this PHP upload tutorial can be download
here. Make sure you change the library/config.php file to match your
own settings

ref: http://www.php-mysql-tutorial.com/php-mysql-upload.php