SQL Understands Microseconds

July 31, 2002 Timothy Prickett Morgan

Hey, Ted:

I am writing regarding your article, “Using Timestamps as Unique Keys ,” which printed on July 17 in Midrange Guru, OS/400 Edition. I would like to add the following option for consideration.

Although the timestamp microsecond value returned by the TIME operation code is only accurate to three positions, SQL’s current timestamp register returns a value accurate to six positions.

To verify this assumption, I created the following simple SQLRPGLE program:

D timestamp1      s               z
D timestamp2      s               z

C                   time                    timestamp1
C/exec sql
C+ set :timestamp2 = current timestamp
C/end-exec
C
C                   eval      *inlr = *on

When I executed this program in debug, I found the two timestamp fields to have the following values:

TIMESTAMP1 = '2002-07-17-07.26.56.573000'
TIMESTAMP2 = '2002-07-17-07.26.56.573256'

Also, if the database file is updated using the SQL UPDATE or INSERT statements, the value can be directly set using the CURRENT TIMESTAMP register. For example, assume a file called paywork, in which the last field is a timestamp field called tstamp:

insert into mylib/paywork
   values(757, 1000.00, 'M', 2, 1, 100.00, 50.00, current timestamp)

update mylib/paywork
   set tstamp = current timestamp
   where pwclock = 900

–Jeff Haddix

Thanks for bringing it up, Jeff. Speaking of INSERT, if you omit the timestamp field from the list of fields, the system inserts a timestamp with six-digit microseconds:

insert into mylib/paywork
   (pwclock, pwgross, pwmarstat, pwnbrdep,
    pwnbrper, pwstatetax, pwlocaltax)
   values(747, 1000.00, 'm', 2, 1, 
   100.00, 50.00)
 

Along the same line, suppose there is a logical file over the paywork file, but this logical file does not include the tstamp field in its field list. If you write to the logical file, the tstamp field will be updated with a value that includes six microsecond digits.

— Ted

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