The DBI code is also fairly simple...You have to set the field separator to be tab instead of the comma default. The easiest way is to treat each file as a separate table, below the file "patients" is the table with the data. There is a fair amount to learn about SQL and the DBI if these are completely new topics. This approach is the most extensible but it is also the most work.

#!/usr/bin/perl -w
use strict;

use DBI;

# csv_sep_char=\t means tab separated, default is a comma of course

my $dbh = DBI->connect("DBI:CSV:csv_sep_char=\t;RaiseError=1")
           or die "Cannot connect: " . $DBI::errstr;
          
my $sth = $dbh->prepare("SELECT * FROM patients
                         WHERE bmi>24 AND bp>135 AND age<30");
                         
$sth->execute();
while (my $row = $sth->fetchrow_arrayref())
{
   print "@$row\n";
}
__END__
Prints:
Jane 50 23 200
Joe 30 22 140

File:patients contains tab separation in real file,
     my editor converts them to spaces here:
name    bmi age bp
Jane    50  23  200
Bob 25  55  120
Norm    28  30  136
Joe 30  22  140
Ben 24  85  110
[download]

Now of course, if this is a "one off" thing, Excel is capable of importing this tab delimited file and the query tool would get you a result set too.