Tuesday, July 06, 2021

How Many Temporal Tables Does Your Site Have?

Sometimes it can be difficult to remember where information is stored in the Db2 Catalog. Usually, with a little rumination and a little review of Appendix A of the IBM Db2 SQL Reference manual (SC27-8859), you can come up with a solution.

For example, I was talking to some DBAs who were trying to remember if they had ever created any business-time temporal tables. A comment was made that we could surely find that in the Db2 Catalog and the conversation moved along... but then I thought, hmmm, let me see what I can do about coming up with a catalog query.

The first step was to think about where this information might be found, which took me to SYSTABLES. A good first thought, but no, it isn't there. So I thought, how about SYSCOLUMNS? And lo' and behold, there was the answer.

The columns identified as the start and end date/time for the temporal range are documented in SYSCOLUMNS in the PERIOD column. PERIOD is defined as a CHAR(1) column and it contains one of the following values for every column defined for each table:

Value Meaning                                                                                    
   B         Column is the start of period BUSINESS_TIME
   C     Column is the end of period BUSINESS_TIME with
    an exclusive endpoint
    I     Column is the end of period BUSINESS_TIME with
    an inclusive endpoint
   S     Column is the start of period SYSTEM_TIME
   T     Column is the end of period SYSTEM_TIME
blank         Column is not used as either the start or the end of
    a period

So using this information, here is a query that will show information about all of the business-time temporal tables you have created:

WHERE  PERIOD IN ('B', 'C', 'I')

If you want to find the system-time temporal tables, just swap out the WHERE clause with this one:

  WHERE PERIOD IN ('S', 'T')  

By becoming adept at querying the Db2 Catalog tables you can find out just about everything you want to know about the databases and objects defined in your Db2 subsystems!

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