On Thu, Feb 13, 2014 at 4:45 AM, Max Vlasov <[email protected]> wrote:
> Hi,
>
> probably was discussed and modified before, but I still can not understand
> some peculiarities with random column values.
>
> The table
> Create table [TestTable] ([id] integer primary key)
>
> populated with 100 default values (thanks to CTE now made with a single
> query):
>
> with recursive
> autoinc(id) as
> (values(1) UNION ALL Select id+1 from autoinc where id < 100)
> insert into TestTable select id from autoinc
>
>
> So the following query
>
> select id, (select id from TestTable where id = abs(random() % 100)) as
> rndid from TestTable where id=rndid
>
> returns a single row (as expected), but this row contains different values
> for id and rndid. I suppose this is because rndid to be shown is calculated
> once, but the one used for comparison is calculated again and again. Is
> this correct behavior?
>
It is undefined behavior, subject to change depending the specific version
of SQLite, compile-time options, optimization settings, and the whim of the
query planner.
By analogy, in C/C++ if you write:
int x = 1;
int y = x++/x++;
What is the value for y? 0, 1, or 2?
--
D. Richard Hipp
[email protected]
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