Question

Does it make any difference to prefer varchar2 over date data type when building data warehouse in Oracle. My data warehouse is not totally warehouse because date dimension is not necessary (no need for date hierarchy) and it is enough to save date as plain ‘MM-DD-YYYY’ formatted string. Which data type to use nevertheless?

Answer 1

Let’s do a little cost/benefit analysis, shall we?

Leave the "date" field as VARCHAR2

Pros:

• Zero computational cost when formatting the date on a report (as long it always appears in the MM-DD-YYYY format).

Cons:

• Cannot be indexed (well, in the chronological sense)
• Searching computation is increased because of TO_DATE calls
• Requires extra computation if the date must appear in a different format on some report (for example: TO_CHAR(TO_DATE(date_column, 'MM-DD-YYYY'), 'DD-MON-YYYY'))
• The column does not require all values to adhere to a particular date format, increasing the risk of a failure if TO_DATE is necessary.

Change the "date" field to DATE

Pros:

• Can be searched upon without the overhead of TO_DATE
• Can be indexed
• "Bad" values cannot be inserted (although the dates may still make no sense from a business perspective)
• Can be easily formatted

Cons:

• I can’t think of anything off the top of my head

Hopefully this will help in your particular decision from a technical perspective. There is always the business (or, office politics) perspective:

date dimension is not necessary

I will fix that for you:

date dimension is not necessary yet

Suppose you leave the column as VARCHAR2 and the client comes along and asks to filter some report on this date field. Suppose this is killing the database server and you finally need to convert it to DATE. Is it relatively easy to make this change in a production environment at your company? Is there plenty of red tape and forms and change control boards you must fight to make your simple change? If you do manage to overcome those hurdles, are you sure that all dates are stored in the same formatting?