Re: A different definition of MINUS, Part 3

vadimtro_at_gmail.com wrote:
...
> Let's move on to other cases. Oracle treats a join view as updatable
> under the following conditions:
>
> *The DML statement must affect only one table underlying the join.
> *For an INSERT statement, the view must not be created WITH CHECK
> OPTION, and all columns into which values are inserted must come from
> a key-preserved table. A key-preserved table is one for which every
> primary key or unique key value in the base table is also unique in
> the join view.
> *For an UPDATE statement, all columns updated must be extracted
> from a key-preserved table. If the view was created WITH CHECK OPTION,
> then join columns and columns taken from tables that are referenced
> more than once in the view must be shielded from UPDATE.
>
> Let's restrict the scope to updates only. Here is a proposition I
> translated these conditions to:
>
> x ^ R00 = dx ^ R00 & % x and dx have the same headers
> (x ^ y) ^ R00 = dz ^ R00 & % x ^ y and dz have the same headers
> (dx ^ x) v R00 = R00 & % dx disjoint with x
> (dx ^ y) v R00 = R00 & % dx "doesn't affect" y
> (dz ^ (x ^ y)) v R00 = R00 & % dz disjoint with x ^ y
> dx = dz v (x ^ R00) -> % dx is a projection of dz
> (x v dx) ^ y = (x ^ y) v dz. % Then, application of increments
> % on the base relations
> % is the same as increment
> % on join view
>
> QBQL exhibits the following counter example
>
> dx =
> {<y=a,x=0,>,<y=b,x=0,>,<y=b,x=2,>,<y=c,x=0,>,<y=c,x=1,>,<y=c,x=2,>,}
> dz =
> {<y=a,x=0,>,<y=b,x=0,>,<y=b,x=2,>,<y=c,x=0,>,<y=c,x=1,>,<y=c,x=2,>,}
> y = {<y=a,x=1,>,}
> x = {<y=a,x=1,>,}
>
> so it must be that I interpreted "The DML statement must affect only
> one table underlying the join" wrong...

I think it's a shame that you had to go to make that translation yourself from conditions that aren't expressed mathematically. Even though I know very little about the language details of Tutorial D, one thing I like very much is how it defines basic features in terms of the algebra. Those terse definitions could allow very quick re-casting of implementation behaviour if a flaw were found. Received on Fri Dec 19 2008 - 21:47:40 CET