Convert To SQL Function! Help!

Can u help me transform this code into sql function?

/* Append modulus 11 check digit to supplied string of digits. */
function GenMOD11( $base_val )
{
$result = "";
$weight = array( 2, 3, 4, 5, 6, 7,
2, 3, 4, 5, 6, 7,
2, 3, 4, 5, 6, 7,
2, 3, 4, 5, 6, 7 );

/* For convenience, reverse the string and work left to right. */
$reversed_base_val = strrev( $base_val );
for ( $i = 0, $sum = 0; $i < strlen( $reversed_base_val ); $i++ )
{
/* Calculate product and accumulate. */
$sum += substr( $reversed_base_val, $i, 1 ) * $weight[ $i ];
}

/* Determine check digit, and concatenate to base value. */
$remainder = $sum % 11;
switch ( $remainder )
{
case 0:
$result = $base_val . 0;
break;
case 1:
$result = "n/a";
break;
default:
$check_digit = 11 - $remainder;
$result = $base_val . $check_digit;
break;
}