Using id and value with jquery autocomplete, javascript, json and php

There are great examples here at jQuery UI: http://jqueryui.com/demos/autocomplete/#remote

Click the view source button below the example to get a look at the Javascript side of things. Note the parameters for "source" (this is the path to your PHP script delivering results) and "minLength." Setting the minLength property to 3 will take care of the second part of your question.

As far as the remote side the results need to be in JSON format so you can query your data from the database, get it as a PHP associative array and then use the json_encode() method to put it into a format that the autocomplete plugin can read. The autocomplete implementation in their example sends a querystring variable, "term", to the source file containing the search string input by the user.

This example expects JSON results from the server to be in this format: [ { "id": "Branta hrota", "label": "Pale-bellied Brent Goose", "value": "Pale-bellied Brent Goose" }, ...]

So the PHP source page could deliver results by using code like this:

// source.php (or whatever path you used for the autocomplete "source" setting)
// Sanitize your input!
$term = mysql_real_escape_string( $_GET['term'] );

$results = mysql_query( "SELECT * FROM employees WHERE name LIKE '%{$term}%' "); // Grab your data

$output_array = new array();

while ( $row = mysql_fetch_assoc( $results ) ) {
    $output_array[] = array( 
        'id' => $row['id']
        , 'label' => $row['name']
        , 'value' => $row['name']
    );
}

// Print out JSON response
echo json_encode( $output_array );

So that's all untested pseudocode, but it should point you in the right direction.