title: Choosing a Database for querying on different combination of fields
body: <p><b>I am looking for the most suitable DB to use for the following requirements:</b><br>
  1) 1 table with ~ 50 million records, ~ 15 columns/fields (strings), no joins are required<br>
  2) query by each combination of the columns is efficient (if required, by creating indexes ahead, but then if reduces update performance and increase size of DB)<br>
  3) after adding a new record, we might also update some fields there later on (efficiency for the update is less important)<br>
  <b>Usages:</b><br>
  return top X (sorted by some fields) for satisfying a query</p>