Build your second query exactly as you would manually

my $col_clause = join(', ', @names);
my $sql  = "SELECT ".$col_clause." FROM ...";
my $sth2 = $dbh->prepare($sql) ...
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This assumes your column names can only be simple identifiers (no spaces, quotes, commas etc). Incidentally, your table design is almost certainly going to cause you trouble later on. That's a topic for a different forum though.