On Wed, Mar 31, 2021 at 9:12 PM Ashutosh Bapat <ashutosh.bapat....@gmail.com> wrote:
> > b). How to present the element > > in UniqueKey. Prue EquivalenceClasses or Mix of Expr and > EquivalenceClass as > > we just talked about. > I think the reason we add ECs for sort expressions is to use > transitive relationship. The EC may start with a single member but > later in the planning that member might find partners which are all > equivalent. Result ordered by one is also ordered by the other. The > same logic applies to UniqueKey as well, isn't it. In a result if a > set of columns makes a row unique, the set of columns represented by > the other EC member should be unique. Though a key will start as a > singleton it might EC partners later and thus thus unique key will > transition to all the members. With that logic UniqueKey should use > just ECs instead of bare expressions. > TBH, I haven't thought about this too hard, but I think when we build the UniqueKey, all the ECs have been built already. So can you think out an case we start with an EC with a single member at the beginning and have more members later for UniqueKey cases? -- Best Regards Andy Fan (https://www.aliyun.com/)
