PHP storing a two dimensional array in a database

I think you can just serialize() the array.  See the notes on the man page here:
http://us2.php.net/serialize

Be sure to escape the serialized data before inserting it - use mysql_real_escape_string() or the equivalent for your DB.

Best, ~Ray

>> what is the best way to store values in a multidimensional an array in a database

The best way is to store it in columns in a table:

create table Messages (userid int,note text);

You should probably have some additional columns, maybe a timestamp? If each user can have only one note, you should have an index on the userid column.

@allanch08: You may be asking a "loaded" question here.  If you have only a small amount of data and you do not need to search it, almost any factually correct answer about how to store it will be acceptable.  By "small amount" I am thinking a few thousand records a day at most.  However if you need the data base capabilities, then you want to think about the structure of the data and in that case, serialize() is maybe not the best approach, since serialize() removes the structure and converts it into a string (albeit a reversable process).  If the underlying question is deeper than what you've posted here, consider "normalization."
http://lmgtfy.com?q=why+should+i+normalize+my+database

Best, ~Ray

Run this, look at the code and output together, and see if it helps clarify what happens here.  Please post back with any questions.  Best regards, ~Ray

<?php // RAY_serialize_unserialize.php
error_reporting(E_ALL);
echo "<pre>\n"; // READABILITY
 
// TEST DATA FROM THE OP
$message = array(
   array('user_id' => '00001', '$msg' => 'Hello'),
   array('user_id' => '00002', '$msg' => 'Goodbye'),
   array('user_id' => '00005', '$msg' => 'Good morning'),
   array('user_id' => '00007', '$msg' => 'Good evening'),
);
 
// SHOW THE INITIAL ARRAY
var_dump($message);
 
// CONVERT THE DATA FORMAT
$s = serialize($message);
echo "SERIALIZED:";
var_dump($s);
 
// ESCAPE THE DATA - IN THE REAL SCRIPT, USE mysql_real_escape_string() INSTEAD OF addslashes()
$e = addslashes($s);
echo "ESCAPED:";
var_dump($e);
 
// UNESCAPE THE DATA - IN THE REAL SCRIPT, THIS HAPPENS WHEN THE DATA GETS INSERTED INTO THE DB
$u = stripslashes($e);
echo "UNESCAPED:";
var_dump($u);
 
// CONVERT SERIAL DATA BACK
$new = unserialize($s);
var_dump($new);
 
// COMPARE
if ($message === $new) echo "\nEQUAL!";

                                              

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Yes - the use of base64encode() changes the length.  You might want to be careful of this since MySQL is length-aware for certain data types (VARCHAR, for example) and may truncate the data.  Other than that, it looks like a good idea.

There is no known bug in unserialize(), the problem described at the blog mentioned above was probably because magic_quotes was enabled, so that addslashes() (or mysql_real_escape_string()) was called twice. There is no problem using the characters ', ", ; or : (or any other characters) in array values when using serialize()/unserialize().

Try like this:

foreach ($message as $msg) {
    echo $msg['user_id'].' '.$msg['msg'].'<br />';
}

                                              

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>> duplicate user_id will result in duplicate keys

PHP prevents duplicate keys, the last assigned array will overwrite the previous with the same key.

No, except if you have multiple messages for the same user. Then only the last one will be stored. This is not the case with how you did it earlier: array('user_id'=>1,'msg'=>'Hello') In this case there can be multiple messages for the same user id.