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List:       kde-bugs-dist
Subject:    [Bug 298197] Kexi crashes while trying to save query with join on non PK fields
From:       Werner Llacer <wllacer () gmail ! com>
Date:       2012-04-22 19:13:33
Message-ID: bug-298197-17878-ranWrHLDGJ () http ! bugs ! kde ! org/
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https://bugs.kde.org/show_bug.cgi?id=298197

--- Comment #9 from Werner Llacer <wllacer@gmail.com> ---
You provided my brand new scar its first good laugh. It did hurt. You had to
pay for it ;-)

Seriously, I really find it has been a sensible idea to provide the educative
bit about lookup tables and foreing keys, virtually lingo-free (most desktop DB
users i've met, don't have the slightest exposure to relational design). I
might be not the target, but it is really a good idea 

Anyway, (per other bug i opened last week) you can only save a query once, so i
will try to stick to the workaround (while very much against my normal usage)
till you can fix it


Why  I'm using non keyed lookup tables, then? A bit of background -and self
justifiying-is not out of place.

The database i'm testing Kexi with is a third party data warehouse  (detailed
Spanish Municipal Elections Results from 2011 if you ever want to know),
originally in MDB, and with a star schema, very odd on first sight. 
In a couple of the lookup tables the natural key is a list of fields, defining
a fixed length hierachy, and lookup can be done on any level of the hierarchy.
In such an scenario, significant primary keys are useless or even
impossible:depending on value spread,the best design query-wise could be to
nullify all component fields thus making a significant primary key inacceptable
for any SQL database.

It is asumed that no self respecting designer would accept a non significative
value in a lookup field (exactly this is the difference with Data Model
Relationship derived foreign keys). To have a real code in the record has saved
many the day ...

An intersting sample is Oracle's smart CG_REF_CODES table for Designer/Forms. A
single table designed to hold  lookup tables, including time constrained or
intervals. The internal PK has absolutely nothing to do with the field value.

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