There are many functions in Crystal with overlapping capabilities, like Val() and ToNumber(). I have always thought of Date and DateSerial as identical functions that both allow you to specify a literal date in a formula by specifying the year, month and day as numbers like this:

Date (2016,11,24)
DateSerial (2016,11,24)

The three numbers can either be literal values, fields or calculations like this:

Date ( {table.Year}, {table.Month} + 2 , 3 )

This will create a date value by taking the Year value from the table, adding two months to the Month value from the table and then taking the 3rd day of that month.

But I just discovered (via a post by AndyMc in Tek-Tips.com) an important difference between the two functions, which is how each function would respond if the value in the field {table.month} was 12.  The Date() function would generate an error because 12 + 2 = 14, which is an invalid month.  The Date() function requires that the month number be from 1 to 12. Also, the day number has to be between 1 and 31 and has to be a number valid within that month.

But the DateSerial() function doesn’t have this limitation. If the formula above used DateSerial(), adding 2 months to month 12 would automatically move forward to next February.  You can also give DateSerial() a day number that is more than 31 and it will move automatically to the next month.

So the The following expression would return 5/1/2016:

DateSerial (2016, 4, 31)

But using Date() would generate an error:

Date (2016, 4, 31)

One of my customers learned a new trick from me today. They wanted a report to automatically select the data for the prior month. They didn’t realized that Crystal has a dedicated function for that and you can use it in both the select expert or in the selection formula. So I figured I would share this, since there may be others that have never seen this function in Crystal.

Go into your select expert and add a rule using any field that is a Date or DateTime. Then in the comparison list look toward the bottom for the option “is in the period”. When you select this option the next drop-down list will automatically populate with 25 pre-programmed functions. You will find items like “LastFullWeek”, “LastFullMonth” and “YearToDate”. These periods are automatically calculated each time you run the report, based on today’s date.
So say you want a report to automatically select the records for the prior month without having to enter the date range or change the report each time. You use the LastFullMonth option in the select expert, or you could do the equivalent, like this, in the selection formula:

{Date.Field} in LastFullMonth

One note, Crystal calculates all of these periods based on the print date which is normally the system date of your computer. But Crystal also allows you to override the system date for any report. Just go to [Report > Set Print Date] and you can pick another date. Just don’t forget to reset the date before you save the report or Crystal will continue to use that same date (for this report) until it is reset.