If you just want a space as a delimiter, the easiest way is to stick the array inside the double quotes and let interpolation take care of it:

open my $OUT, '>>', "$mycrdir/file_detail.txt" or die "Can't create '$
+mycrdir/file_detail.txt'" ;
while (my @row = $sth->fetchrow_array) {
    print $OUT "@row\n";
}
close $OUT;
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If you need a comma or anything more exotic, use join as described elsewhere in the thread