Proper Comparisons for Dates in Merge Fields

Volker is having a problem comparing dates in a merge field. His database contains a Birthdate field, which (obviously) contains a birth date for each person in the database. As he merges each record, he wants to compare the Birthdate field to a reference date, and then take some action based on the result. The logic he is attempting to use looks like this:

{IF {MERGEFIELD Birthdate} > "10/4/1976" "Under 30" "Over 30"}

The problem is that the comparison doesn't work properly; it doesn't return consistent results. One possible solution is to use a format switch in the merge field, in the following manner:

{IF {MERGEFIELD Birthdate\@"MM/DD/YYYY"} > "10/04/1976" "Under 30" "Over 30"}

This puts the incoming information into a comparable format. The results you get from this approach may depend, however, on characteristics of the data source, independent of Word. You could also try putting the dates into a year-first format, such as the following:

{IF {MERGEFIELD Birthdate\@"YYYY/MM/DD"} > "2006/10/04" "Under 30" "Over 30"}

If the comparison still yields inconsistent results, then the only solution may be to do a mathematical conversion on the date (actually, on both Birthdate and the reference date) so that you have an actual numeric comparison. You can do this by converting the date into a Julian value, which requires a very complex merge field, like the one shown here:

{IF {QUOTE {SET a{=INT((14-{MERGEFIELD BIRTHDATE \@ M})/12)}}
{SET b{={MERGEFIELD BIRTHDATE \@ yyyy}+4800-a}}
{SET c{={MERGEFIELD BIRTHDATE \@ M}+12*a-3}}
{SET d{MERGEFIELD BIRTHDATE \@ d}}
{SET jd{=d+INT((153*c+2)/5)+365*b+INT(b/4)-INT(b/100)+INT(b/400)-32045}}
{jd \#,0}} > 2,443,056 "over 30" "under30"}

Such an approach may look intimidating, but is just the brute-force method necessary for some instances. If you want more details on how the conversion works (and why it may be necessary), check out the following file:

http://www.wopr.com/w3tfiles/10-249902-DateCalc.zip

When you uncompress this file, you end up with a Word document that includes the full, multi-page explanation concerning date conversions.