> > Can somebody help me with the syntax of EVAL. I want to execute a
> > SELECT on a file to get all records where (field 16)*0.9 <
> field(17).
>
> Various ways to do this. Try...
> SELECT file WITH EVAL "F16 * 0.9 < F17" = 1
> where F16 and F17 are field names from the dictionary.
>
> The most common mistake is to miss off the = 1 at the end.
> Remember, this EVAL expression is going to return true or false.
1. Yes, but put quotes around the final literal 1:
WITH EVAL "F16 * 0.9 < F17" = "1"
or it will try to find a record called "1" in both the dictionary and
VOC. Many Pick-style dicts have that. Even if it doesn't exist today,
it might in the future.
2. You might be tempted to do:
WITH EVAL "F16 * 0.9" < F17
(or WHEN '' '' '' '' for multivalued data)
which will probably work, but with EVALs you sometimes need to include
explicit formatting & conversion on the command line. RetrieVe
sometimes outsmarts itself when sorting BY an EVAL or using an EVAL as a
display column. By default it sometimes assigns to the EVAL the
conversion & justification of an element inside the EVAL. Annoying,
that. All this makes Martin's answer better, since it is more
explicit.
3. If you use Pick-style dictionaries, you can still use EVALs, and you
can extract the fields you want:
WITH EVAL "@RECORD<16> * 0.9 < @RECORD<17>" = "1"
4. All this assumes single-valued fields, right? Let us know, because
if either F16 or F17 are multi-valued, you'll need a variation on the
theme by using "LTS" function and/or the WHEN keyword.
Chas. Stevenson
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