1. 22BI Creating SQL Functions
Greg Cannella

2. Functions let you transform data from the way it is stored in the database to the way you want to use or see it.

3. Agenda Why functions? Examples Create function Drop function
How to see and manage existing functions
Handling NULL

4. Why functions? Fix the sins of your predecessors!
Make SQL do new things
Use complex routines
Helps to keep SQL simple
Simplify routine tasks

5. Examples Convert date from DB format to user format
Select datemdy(dbdate) from xyzfile
This example converts from to 10/21/15

6. Examples Pricing Routines 1000s of lines of existing code
Select price(customer,item,date) from xyzlist
Create a stub service program that simply calls your existing code

7. Examples Create a hyper link
<a href="
Select link(url,urltext) from websitelst
-OR-
select CONCAT(concat(Concat('<a href="',TRIM(url)), concat('">',TRIM(urltext))), '</a>') from websitelst

8. Built in Functions List of DB2 functions (just the common ones)
Count, Min, Max, Sum, Char, CurDate, CurTime, Hex, Left, Length, Coalesce
Substr, Day, Date, Lower, Upper, Right, Round, RRN, Trim
Complete list of built in functions:
h2func.htm

9. Create Function Statement
CRTSRVPGM SRVPGM(QGPL/DATEMDY) EXPORT(*ALL)
Then STRSQL and run the following SQL command.
create function LIBRARY.DATEMDY
(cyymmdd numeric(7,0) default 0)
returns char(8)
language rpgle
deterministic
no sql
external name ‘QGPL/DATEMDY(DATEMDY)'
parameter style general

10. Unpacking the create function
Parameters
In this example:
(cyymmdd numeric(7,0))
A single parm is passed into the function
For multiple parms the syntax is:
(dbname char(128),
Parm2 char(10),
Parm3 numeric(7,0))
Parameters go into the function but don’t come back.

11. Unpacking the create function
Returns
This needs to match the value coming back from the service program. This needs to match exactly. Also note that SQL data types can differ from RPG data types.
If the type doesn’t match exactly, you will get a function not found error when trying to use the function.

12. Unpacking the create function
Language
You can use any language available on the platform to create functions
These can have embedded SQL or not.

13. Unpacking the create function
Deterministic
Use ‘not deterministic’ if the same parameters might return different results.
Example: The function returns the number of jobs waiting to run in a JOBQ.
Use ‘deterministic’ if the function will always return the same value for the same values
Example: The function accepts in a date and returns the day of the week.

14. Unpacking the create function
SQL – Probably the most important. This needs to match how your function works.
READS SQL DATA – Prevents the underlying function from modifying data in the database
CONTAINS SQL – Allows a very limited set of “non-executable” SQL statements.
NO SQL – The underlying function can’t run any SQL.
MODIFIES SQL DATA – The underlying function can run SQL statements that updates, inserts, deletes, or reads data.

15. Unpacking the create function
External name
This is the name of the service program and module
Syntax: library/Servicepgm(Module)
Example: gregc/datemdy(datemdy)

16. Unpacking the create function
Parameter style
I just use ‘parameter style general’
These cause the parameters to function very much like RPGLE service programs.
There is also SQL, DB2GENERAL, JAVA, DB2SQL.

17. Recap create function create function LIBRARY.DATEMDY
(cyymmdd numeric(7,0) default 0)
returns char(8)
language rpgle
deterministic
no sql
external name ‘QGPL/DATEMDY(DATEMDY)'
parameter style general

18. Drop Function
drop function library.datemdy

19. Managing Functions Navigator for I
Navigate to the schema where your functions are stored
Click on functions

20. Navigator for i Select a function Actions Definition
This will allow you to see and modify everything about the function definition.

21. Handling Errors and NULL
Check your parms upon entry
Monitor for bad data
Select a default value if failure
Datemdy(coalesce(field1,0))

22. Function Not Found Error
Check the library
Check the spelling
Check that the parameters match (Functions allow overloading.)
7.1 Doesn’t cast variables as well as You may need to force type your parameters.

23. Recap Use functions to transform data Create function Drop function
Navigator for managing functions

24. Thank you
Questions?

25. For more info on functions
Create functions
fsc.htm
Built in functions
h2func.htm

26. Sample Convert Date Program
ctl-opt option(*srcstmt:*nodebugio) Debug nomain alwnull(*usrctl) ; // Compile Options: * // Create this as a module. * // CRTSRVPGM SRVPGM(MAGID/DATEMDY) EXPORT(*ALL) * // Then start SQL and run the following SQL command. * // create function magid.DATEMDY * // (cyymmdd numeric(7,0) default 0) * // returns char(8) * // language rpgle * // deterministic * // no sql * // external name 'MAGID/DATEMDY(DATEMDY)' * // parameter style general * //--Entry Prototype dcl-pr DATEMDY char(8); DateIn zoned(7:0) OPTIONS(*NOPASS); end-pr; dcl-proc DATEMDY export ; dcl-pi DATEMDY char(8); end-pi; dcl-s WorkDate date(*iso); dcl-s DateOut char(8); //-- Convert date from CYYMMDD to MM/DD/YY c Eval DateOut = *blanks c Monitor c *cymd Move DateIn WorkDate c *mdy Move WorkDate DateOut c On-error c Endmon return DateOut; end-proc;

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