[tarantool-patches] Re: [PATCH] sql: assertion fail on nested select
alexander.turenko at tarantool.org
Tue Jul 17 16:59:34 MSK 2018
Please, consider comments below.
WBR, Alexander Turenko.
On Mon, Jul 02, 2018 at 03:11:40PM +0300, N.Tatunov wrote:
> To optimize the select-subquery tarantool uses
> subquery flattening function which is only used
> with respect to some restrictions. One of them
> was implemented improperly.
Be certain: 'some restriction' and just 'improperly' are not good
I would use wording like the following.
> When a subquery is a compound select the subquery flattening
> optimization verify whether the ORDER BY clause presents, but only for
> the last subquery component. The commit fixes that to verify all
> subquery components.
> In case of ORDER BY in non-last component of a compound select the
> error should be raised. Accepting of such subqueries for the
> flattening optimization prevents the error to be raised afterwards.
> Instead it stuck into assertion violation inside flattenSubquery (see
> the issue).
I checked sqlite3 check-in 8000d230 (it is immediate predecessor of
c9104b59 where the flattening optimization seems to be changed, but
tarantool didn't updated with that check-in). It has the assert, but has
no a change like yours, and correctly shows the following error:
Error: ORDER BY clause should come after UNION ALL not before
Why it is so?
> + "subquery-9.3",
> + [[
> + SELECT * FROM (SELECT * FROM table1 ORDER BY 1 UNION All
> + SELECT * FROM table1 UNION All
> + SELECT * FROM table1);
All -> ALL
More information about the Tarantool-patches