Why a chain have the same size applying gzcompress and gzuncompress?

i have a mysql table with a field and i don't have the permission to modify the table schema.

content varchar (255) not null

is there anyway to insert string with more size(greater than 255) to this field.i dont care how its stored(compressed or encoded).i want to retrieve the uncompressed one if it is compressed.

things i tried

gzcompress();

base64_encode();

<?php
$compressed   = gzcompress('asdasdwq3eryt238774284873246827364872687342873rweuydfgjshdbfdgfgs', 9);
$uncompressed = gzuncompress($compressed);
echo $compressed.'---'.strlen($compressed);
echo "<br />";
echo $uncompressed.'----'.strlen($uncompressed);

//BOTH ARE SAME IN SIZE
?>