php get the first part of postcode

I need to extract the first part of postcode for search calculation using a database. Any ideas?! I need this to implement a search module in the site, which looks out for some relevant information according to the post code. But the database which I am having for post code, it doesnt have second part of the postcode, only the first part is th开发者_开发技巧ere. Its for UK postcode. So, any ideas?!

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This will not cover 100% of all possible UK postcodes, but will do for like 99.999% or so :)

/**
 * @param string $postcode UK Postcode
 * @return string
 */
function getUKPostcodeFirstPart($postcode)
{
    // validate input parameters
    $postcode = strtoupper($postcode);

    // UK mainland / Channel Islands (simplified version, since we do not require to validate it)
    if (preg_match('/^[A-Z]([A-Z]?\d(\d|[A-Z])?|\d[A-Z]?)\s*?\d[A-Z][A-Z]$/i', $postcode))
        return preg_replace('/^([A-Z]([A-Z]?\d(\d|[A-Z])?|\d[A-Z]?))\s*?(\d[A-Z][A-Z])$/i', '$1', $postcode);
    // British Forces
    if (preg_match('/^(BFPO)\s*?(\d{1,4})$/i', $postcode))
        return preg_replace('/^(BFPO)\s*?(\d{1,4})$/i', '$1', $postcode);
    // overseas territories
    if (preg_match('/^(ASCN|BBND|BIQQ|FIQQ|PCRN|SIQQ|STHL|TDCU|TKCA)\s*?(1ZZ)$/i', $postcode))
        return preg_replace('/^([A-Z]{4})\s*?(1ZZ)$/i', '$1', $postcode);

    // well ... even other form of postcode... return it as is
    return $postcode;
}

Test data:

echo 'TW135BQ -> ', getUKPostcodeFirstPart('TW135BQ'), "\n";
echo 'gir0aa -> ', getUKPostcodeFirstPart('gir0aa'), "\n";
echo 'RG5 3SQ -> ', getUKPostcodeFirstPart('RG5 3SQ'), "\n";
echo 'AB51 0GQ -> ', getUKPostcodeFirstPart('AB51 0GQ'), "\n";
echo 'YO104EA -> ', getUKPostcodeFirstPart('YO104EA'), "\n";
echo 'SE154NS -> ', getUKPostcodeFirstPart('SE154NS'), "\n";
echo 'W1B4BD -> ', getUKPostcodeFirstPart('W1B4BD'), "\n";

Results:

TW135BQ -> TW13
gir0aa -> GIR0AA
RG5 3SQ -> RG5
AB51 0GQ -> AB51
YO104EA -> YO10
SE154NS -> SE15
W1B4BD -> W1B

Please note: It is your responsibility to provide valid postcode.

EDIT: oops, it does not cover GIR 0AA, sorry