RE: when to use a function or file for information

-----Message d'origine-----
De : midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] De la part de Birgitta Hauser

The other advantage when selecting the data you need, is the
query optimizer may use an IOA (Index Only Access), that
means an index or logical file can found where all requested
information is stored in the key fields, so no further access
to the data base record is needed. IOA is the fastest method
to access data. When using SELECT * an IOA will not be possible.

Do you mean if I have select clientnumber and an index on clientnumber the table will not be used, only the index?
Whereas if I had select *, I would need an index on all the fields for this to happen?

The other advantage when using field selection instead of
SELECT *, you can enhance your table without any need to
recompile your programs. When using SELECT * you may need an
(external) data structure to hold the information and this
data structure layout will included at compile time into your
program object. To get the current data structure/file layout
included, you need to recompile your programs.

I think the idea is that if the file structure changed and the select used one of the changed fields, then the program may have to be modified depending on how the result set ds has been declared. If myfile is changed, our <CMS> will detect all programs with extname(myfile) and recompile them.