Date range comparison using varchar columns in Teradata - sql

Question

I've been tasked to take a calendar date range value from a form front-end and use it to, among other things, feed a query in a Teradata table that does not have a datetime column. Instead the date is aggregated from two varchar columns: one for year (CY = current year, LY = last year, LY-1, etc), and one for the date with format MonDD (like Jan13, Dec08, etc).
I'm using Coldfusion for the form and result page, so I have the ability to dynamically create the query, but I can't think of a good way to do it for all possible cases. Any ideas? Even year differences aside, I can't think of anything outside of a direct comparison on each day in the range with a potential ton of separate OR statements in the query. I'm light on SQL knowledge - maybe there's a better way to script it in the SQL itself using some sort of conversion on the two varchar columns to form an actual date range where date comparisons could then be made?

Answer 1

Here is some SQL that will take the VARCHAR date value and perform some basic manipulations on it to get you started:
SELECT CAST(CAST('Jan18'||TRIM(EXTRACT(YEAR FROM CURRENT_DATE)) AS CHAR(9)) AS DATE FORMAT 'MMMDDYYYY') AS BaseDate_
, CASE WHEN Col1 = 'CY'
THEN BaseDate_
WHEN Col1 = 'LY'
THEN ADD_MONTHS(BaseDate_, -12)
WHEN Col1 = 'LY-1'
THEN ADD_MONTHS(BaseDate_, -24)
ELSE BaseDate_
END AS DateModified_
FROM {MyDB}.{MyTable};
The EXTRACT() function allows you to take apart a DATE, TIME, or TIMESTAMP value.
You have you use TRIM() around the EXTRACT to get rid of the whitespace that is added converting the DATEPART to a CHAR data type. Teradata is funny with dates and often requires a double CAST() to get things sorted out.
The CASE statement simply takes the encoded values you suggested will be used and uses the ADD_MONTHS() function to manipulate the date. Dates are INTEGER in Teradata so you can also add INTEGER values to them to move the date by a whole day. Unlike Oracle, you can't add fractional values to manipulate the TIME portion of a TIMESTAMP. DATE != TIMESTAMP in Teradata.

Answer 2

Rob gave you an sql approach. Alternatively you can use ColdFusion to generate values for the columns you have. Something like this might work.
sampleDate = CreateDate(2010,4,12); // this simulates user input
if (year(sampleDate) is year(now())
col1Value = 'CY';
else if (year(now()) - year(sampleDate) is 1)
col1Value = 'LY'
else
col1Value = 'LY-' & DateDiff("yyyy", sampleDate, now());
col2Value = DateFormat(sampleDate, 'mmmdd');
Then you send col1Value and col2Value to your query as parameters.