I offer the following monstrosity up, as a sacrifice to Timmy Toady (TMTOWTDI):

$/ = undef or
$data = <> and
$data =~ s{
    ^TABLE;([^;\n]+).*$
    |
    ^COLUMN;(.+?);.*$
}{$1 ? (($t=$1),"") : "$t.$2"}mexg;

print $data;
[download]

Or condensed to uglier form:

perl -e '$/=undef or $_=<> and s{^TABLE;([^;\n]+).*$|^COLUMN;(.+?);.*$
+}{$1?(($t=$1),""):"$t.$2"}mexg and print;' data.txt
[download]

Update - golfed

perl -e'local$/or$_=<>,s{^TABLE;(.+?)$|^COLUMN;(.+?);.*$}{$1?(($t=$1),
+""):"$t.$2"}mexg and print;' data.txt
[download]

Wait.. was this in the SoPW or obfu section? :)