SQL REPLACE with pointer

2555 pts.
AS/400 SQL
SQL Server
I need to manipulate xml-files larger than char-field max-length allowed with RPG.


[strong]Background info:[/strong]

My current solution uses a char-field...

My app stores XML-files in CLOB-fields. I copy the xml-file from CLOB-field to a char-field: [code] /free    exec sql SELECT MyCLOBfield INTO :myfield  FROM...etc [/code] I then use %scan to find relative position of the string to be replaced, which is done using the %replace bif. Since multiple occurrences of the string to be replaced may exist, I proces the %scan and %replace in a loop untill all occurrences has been replaced.

[strong]I discovered...[/strong]

With SQL it is possible to replace all occurrences in one step (ie statement), which this small RPG test-pgm proves: [code] d myfield         s            1000  /free     exec sql DECLARE :myfield VARIABLE;     exec sql SET :myfield = 'xxx bbb ccc bbb ccc aaa';     exec sql SET :myfield = REPLACE(:myfield, 'bbb', 'xxx');     // myfield now contains 'xxx xxx ccc xxx ccc aaa''.     *inLR = *on; [/code]

As can be seen, SQL makes multiple replace's, thus eliminating the need of a programmed loop.

[strong]My challenge:[/strong]

The xml-files I recieve from outside my company tends to be bigger and bigger, and I foresee that my current solution will break down soon. Therefore I want to re-write the code to use pointers. So far, I have this in place:     1. I copy the xml-file from CLOB-field to memory using SQL SELECT multiple fragments (32K at a time) and append the fragment to the xml-string in memory using a pointer.     2. I have RPG-code in place to do the scan/replace task, but I'd like to do this part with sql as well.

[strong]My question:[/strong]

Is it possible to use SQL with pointer to make a 'multi-replace'like the way I discovered (see above) it can be done with a char-field. ?






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  • carlosdl
    Dan, maybe I'm missing something, but how about using the REPLACE function in your SELECT statement where you copy the xml-file from CLOB to memory ? Something like this:
    exec sql SELECT REPLACE(MyCLOBfield,'bbb', 'xxx') INTO :myfield  FROM...
    It could produce a type mismatch if the REPLACE function is not allowed on CLOB fields, and maybe that is why you are not doing it that way.
    85,390 pointsBadges:
  • TomLiotta
    That's such an elegant suggestion that I've hardly been able to focus on the question. Nice! Still, the {INTO :myfield} part is where some difficulty arises. There is no facility for declaring the :myfield host variable big enough in the host language. COBOL allows up to 16711568 bytes for an alphanumeric item, REXX allows at least that much, and C is similar to COBOL. But RPG has a limit in that area -- basically it's 64K. (Of course, CL is only 32K.) Maybe as a DS with an array of subfields? I haven't tried it. However, this is also a good candidate for a service program procedure. It seems like a function that could be used in many places. Maybe looking for a way to code it into a program with very few lines isn't the right approach. Tom
    125,585 pointsBadges:
  • DanTheDane
    Carlos, Tom points it out clearly what the issue is in using your sql-solution (which I like very much..), namely that the SQL INTO requires a field (limited length!!), which is why I move data in chuncks of 32000 from my CLOB-field into memory. I will follow Tom's recommandation to isolate the scan/replace in a servicepgm. Hmmmm, - maybe use another language for this servicepgm!! ?? I am considering a procedure interface something like this:
    D ScanRpl         PI                   
    D  Pointer                        *    
    D  StartOffset                   9  0  
    D  EndOffset                     9  0  
    D  ToBeReplaced              64000     
    D  ReplaceWith               64000     
    D  Returncode                    7 
    StartOffset and EndOffset shall both be optional parameters. Any thoughts on alternative language for the servicepgm are most welcome. DanF
    2,555 pointsBadges:

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