title: Should date field in DW date-map be of Date data type or of String data type, if I want to put placeholders?
body: <p>I have a date map (date dimension) like every other data warehouse.</p>
  
  <p>The most obvious way to store date field in the date field is in date datatype. However, I want to keep some records in my date dimension which ID as negative values and the date field should give description of why this date is invalid.</p>
  
  <p>For example, in my fact table, let's say I have a field called order_date_id which references the date dimension. However, for some records in the fact table, I want to say that the order_date was not recorded by the system and hence we can't use it. But I want it's entry present.</p>
  
  <p>I thought that I would make an entry in the date dimension with ID=-1 and date = 'Date was not recorded'. But to use this kind of a placeholder, I will have to keep date as a string value. If I store it as a string value it will be very ineffective when I compare two dates.</p>
  
  <p>Please advise a good practice.</p>