DB<101> @columns=qw(firstname middlename lastname)
 => ("firstname", "middlename", "lastname")

  DB<102> @colidx{@columns}=0..$#columns
 => (0, 1, 2)

  DB<103> $colidx{middlename}
 => 1

  DB<104> \%colidx 
 => { firstname => 0, lastname => 2, middlename => 1 }