title: A table with many null value vs 2 separate tables
body: <p>I have a table (X) with 10 columns, 6 of which are nullable foreign keys (bigint data type) and in every row 5 of them will be NULL. </p>
  
  <p>SOLUTION: Divide table (X) into 2 tables: (X) and (XType) so that (X) includes a big int column (not foreign key) for insert one of six <code>ID</code> and a <code>XType_id</code> column for determining types of 6 data. </p>
  
  <p>Is this solution optimal or the first table with 10 columns is better?</p>