Let's review of some of the SQL functions available.
In the February 2015 CL Corner, A More Flexible Interface to the RUNSQL CL Command, we saw how to create a command of our own, CRTSQLVIEW, to create views by utilizing some of the built-in functions provided by the SQL language. The CRTSQLVIEW command removed the need for us to write a custom program per view (which was covered in the January 2015 article Enhancing WRKQRY Reports the Easy Way. These previous articles used the SQL built-in functions of VarChar and DayName to return the mixed-case name of the day for a date field. This month, using CRTSQLVIEW, we'll be looking at additional built-ins that are available to you.
Deciding which built-in to start with today turned out to be quite easy. I have received quite a few notes from readers who have a little problem—namely, that the previous articles used date fields while their production databases store dates in a combination of alphanumeric and packed-decimal fields. To look at what's available using a view approach, we'll first create a new physical file where we're storing date values using a variety of formats and data types. This file will be called TESTDATA, and here's the DDS definition for the file.
R RECORD
DATFLD L
MDYALPHA 6A
YMDALPHA 6A
MDYNBR 6P 0
The first field, DatFld, is defined as a date field, which is similar to how we defined TskStrDat in the previous articles. The second field, MDYAlpha, is defined as a 6-byte character field and will be used to store date values using a MDY format. The third field, YMDAlpha, is defined as a 6-byte character field and will be used to store date values using a YMD format. The fourth field, MDYNbr, is defined as a 6-digit packed-decimal field and will be used to store date values using a MDY format.
Assuming that the previous source is stored in member TESTDATA of QDDSSRC, then you can create the file using this command:
CRTPF FILE(TESTDATA)
To write two test records to the file, prompt and then run the following RUNSQL commands:
Run SQL Statements (RUNSQL)
Type choices, press Enter.
SQL . . . . . . . . . . . . . . > Insert into TESTDATA Values('2015-03-21', '0
32115', '150321', 032115)
...
Commitment control . . . . . . . > *NONE *CHG, *UR, *CS, *ALL, *RS...
Naming . . . . . . . . . . . . . *SYS *SYS, *SQL
Run SQL Statements (RUNSQL)
Type choices, press Enter.
SQL . . . . . . . . . . . . . . > Insert into TESTDATA Values('2015-12-25', '1
22515', '151225', 122515)
...
Commitment control . . . . . . . > *NONE *CHG, *UR, *CS, *ALL, *RS...
Naming . . . . . . . . . . . . . *SYS *SYS, *SQL
The first command writes one record with the date March 21 2015 stored in each of the four fields defined to TESTDATA. The second command writes a second record using the date December 25 2015.
Now let's see what we can do to get those non-date data type fields MDYAlpha, YMDAlpha, and MDYNbr to become "true" date fields.
We'll first tackle the alphanumeric fields MDYAlpha and YMDAlpha. SQL provides the built-in TIMESTAMP_FORMAT, which returns a timestamp that's based on a string definition of how to interpret an input character value. This string definition allows you to indicate where in the input character value to find, among other things, a 2-digit year (YY), a 4-digit year (YYYY), a 2-digit month (MM), and a 2-digit day (DD). For instance, using TIMESTAMP_FORMAT as in
TIMESTAMP_FORMAT(MDYAlpha, 'MMDDYY')
indicates that the field MDYAlpha contains a formatted value that should be converted to a timestamp, where the first two bytes identify a 2-digit month, the next two bytes a 2-digit day, and the last two bytes a 2-digit year. So a MDYAlpha value such as '032115' (like the first record we wrote to TESTDATA) would be converted to a timestamp value of '2015-03-21-00.00.00.00000'.
Along the same lines, using TIMESTAMP_FORMAT as in
TIMESTAMP_FORMAT(YMDAlpha, 'YYMMDD')
indicates that the field YMDAlpha contains a YMD formatted value that should be converted to a timestamp. A YMDAlpha value such as '151225' (like the second record we wrote to TESTDATA) would then be converted to a timestamp value of '2015-12-25-00.00.00.000000'.
With that introduction let's now use CRTSQLVIEW to create a view, using the fields MDYAlpha and YMDAlpha, to again determine the name of the day they represent. Prompt and fill in the CRTSQLVIEW command as shown below:
Create SQL View (CRTSQLVIEW)
Type choices, press Enter.
View . . . . . . . . . . . . . . > TESTVIEW Name
Library . . . . . . . . . . . *CURLIB Name, *CURLIB
Table . . . . . . . . . . . . . > TESTDATA Name
Library . . . . . . . . . . . *LIBL Name, *LIBL, *CURLIB
Columns:
To column . . . . . . . . . . > DATFLD Name
From . . . . . . . . . . . . . *SAME
To column . . . . . . . . . . > DATFLDDOW Name
From . . . . . . . . . . . . . > Varchar(DayName(DatFld), 10)
To column . . . . . . . . . . > MDYDOW Name
From . . . . . . . . . . . . . > Varchar(DayName(Timestamp_Format(MDYAlpha,
'MMDDYY')), 10)
To column . . . . . . . . . . > YMDDOW Name
From . . . . . . . . . . . . . > Varchar(DayName(Timestamp_Format(YMDAlpha,
'YYMMDD')), 10)
The previous command creates a view named TESTVIEW. If you now go into WRKQRY, select the file TESTVIEW, and use F5 to run the query, you should see this:
DATFLD DATFLDDOW MDYDOW YMDDOW
000001 2015-03-21 Saturday Saturday Saturday
000002 2015-12-25 Friday Friday Friday
As with the two earlier articles, the first column (titled DATFLD) is simply the value of the DatFld field followed by the day of the week (DATFLDDOW). What's new is that now we also see the day of the week for the alphanumeric fields MDYAlpha (MDYDOW) and YMDAlpha (YMDDOW).
Before handling the packed-decimal field MDYNbr, let's also see how we might be able to simplify existing queries that have been working with alphanumeric "date" fields such as MDYAlpha and YMDAlpha. Some of you may in the past have constructed date fields within WRKQRY such as the MyDate field shown below.
Field Expression Column Heading Len Dec
MYDATE Date(Substr(MDYAlpha, 1, 2) || '/
' || Substr(MDYAlpha, 3, 2) || '/
' || Substr(MDYAlpha, 5, 2))
While you can continue to construct date fields in this manner, you could also have CRTSQLVIEW do it using the SQL DATE built-in. For instance, adding the following COLUMNS entry to our previous command will create the field MyDate in TESTVIEW, allowing you to eliminate the construction shown above.
Columns:
To column . . . . . . . . . . > MYDATE Name
From . . . . . . . . . . . . . > Date(Timestamp_Format(MDYAlpha, 'MMDDYY'))
Returning to the handling of "date" values being stored in numeric fields, the TIMESTAMP_FORMAT built-in only supports an input character value for the "date" to be interpreted. So what we need to do is convert the numeric field MDYNbr to a character string. There are several SQL built-ins that can accomplish this, with each of them having slightly different characteristics. There is, for instance, the built-in CHAR, which is often used as it returns a fixed-length character string representation of a number. This built-in, however, has a definite consideration when it comes to handling numeric values—namely, that it removes leading zeroes. So if we have a numeric value such as 032115 (the value of MDYNbr for the first record we wrote to TESTDATA), the CHAR built-in will return a character value of '32115' rather than a value of '032115'. This will be a problem as TIMESTAMP_FORMAT is looking for a 2-digit month (though a MDYNbr value of 122515 would work just fine). As the number of significant digits in a numeric date can vary, we will want to use the DIGITS built-in. DIGITS returns the character-string representation of the absolute value of a number and retains leading zeroes.
With this knowledge, we can now get the day of the week for MDYNbr by adding another column definition to our CRTSQLVIEW command. This addition will be:
Columns:
To column . . . . . . . . . . > MDYNBRDOW Name
From . . . . . . . . . . . . . > Varchar(DayName(Timestamp_Format(Digits(MDYN
br), 'MMDDYY')), 10)
This 'From' parameter value is a nesting of several SQL built-ins that result in:
- Getting the absolute value of MDYNbr, with leading zeroes, using DIGITS
- Converting the value obtained in step 1 to a date using TIMESTAMP_FORMAT, interpreting this value as being MMDDYY
- Obtaining the date portion of the value obtained in step 2 and getting the name of that day using DAYNAME
- Truncating the name of day value obtained in step 3 to the first 10 characters using VARCHAR
Today, we have reviewed several additional built-ins that can used from CL to create views over data, views that can in turn be used by utilities such as WRKQRY or processed as an input file by a CL program. The built-ins introduced were TIMESTAMP_FORMAT (which can also be accessed using the name TO_DATE if you prefer less typing, though note that all of the Information Center documentation is found under the name TIMESTAMP_FORMAT), DATE, CHAR, and DIGITS. We have only touched on what all could be used, though in terms of the built-ins found here, so I encourage you to review what's possible.
More CL Questions?
Wondering how to accomplish a function in CL? Send your CL-related questions to me at
Bruce Vining is president and co-founder of Bruce Vining Services, LLC, a firm providing contract programming and consulting services to the System i community. He began his career in 1979 as an IBM Systems Engineer in St. Louis, Missouri, and then transferred to Rochester, Minnesota, in 1985, where he continues to reside. From 1992 until leaving IBM in 2007, Bruce was a member of the System Design Control Group responsible for OS/400 and i5/OS areas such as System APIs, Globalization, and Software Serviceability. He is also the designer of Control Language for Files (CLF).A frequent speaker and writer, Bruce can be reached at
MC Press books written by Bruce Vining available now on the MC Press Bookstore.
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