PHP function to build query string from array

I'm looking for the name of the PHP function to build a query string from an array of key value pairs. Please note, I am looking for the built in PHP function to do this, not a homebrew one (that's all a google search seems to return). There is one, I just can't remember its name or find it on php.net. IIRC its name isn't that intuitive.

You're looking for http_build_query().

Here's a simple php4-friendly implementation:

/**
* Builds an http query string.
* @param array $query  // of key value pairs to be used in the query
* @return string 	   // http query string.
**/
function build_http_query( $query ){
	
	$query_array = array();
	
	foreach( $query as $key => $key_value ){
	
		$query_array[] = urlencode( $key ) . '=' . urlencode( $key_value );
		
	}
	
	return implode( '&', $query_array );

}

Just as addition to @thatjuan's answer.
More compatible PHP4 version of this:

if (!function_exists('http_build_query')) {
    if (!defined('PHP_QUERY_RFC1738')) {
        define('PHP_QUERY_RFC1738', 1);
    }
    if (!defined('PHP_QUERY_RFC3986')) {
        define('PHP_QUERY_RFC3986', 2);
    }
    function http_build_query($query_data, $numeric_prefix = '', $arg_separator = '&', $enc_type = PHP_QUERY_RFC1738)
    {
        $data = array();
        foreach ($query_data as $key => $value) {
            if (is_numeric($key)) {
                $key = $numeric_prefix . $key;
            }
            if (is_scalar($value)) {
                $k = $enc_type == PHP_QUERY_RFC3986 ? urlencode($key) : rawurlencode($key);
                $v = $enc_type == PHP_QUERY_RFC3986 ? urlencode($value) : rawurlencode($value);
                $data[] = "$k=$v";
            } else {
                foreach ($value as $sub_k => $val) {
                    $k = "$key[$sub_k]";
                    $k = $enc_type == PHP_QUERY_RFC3986 ? urlencode($k) : rawurlencode($k);
                    $v = $enc_type == PHP_QUERY_RFC3986 ? urlencode($val) : rawurlencode($val);
                    $data[] = "$k=$v";
                }
            }
        }
        return implode($arg_separator, $data);
    }
}

Implode will combine an array into a string for you, but to make an SQL query out a kay/value pair you'll have to write your own function.