Hi Danny, Thanks for updating the documentation, I really like this design. But I have two more suggestions:
1) As "STORED" keyword is not in the MVP, I would like to remove the optional "[VIRTUAL]" keyword as well. Because this optional keyword is useless for now, all the computed columns are virtual as default. If we add this optional keyword in the syntax, users may have the feeling that the default is the opposite mode "STORED" (the optional "[NOT NULL]" keyword works in this way), however the default is virtual which may surprise users. 2) Not introduce `GenerationStrategy` class for now. I think the design of `GenerationStrategy` is really good. However, the same reason as above, "STORED" is not introduced in the MVP. Then this class is useless (all computed columns are virtual). We can introduce this class once we support "STORED". And I think this is a safer way than rushing to expose some APIs users don't need yet. What do you think? Best, Jark On Fri, 25 Oct 2019 at 21:11, Kurt Young <ykt...@gmail.com> wrote: > The updated doc looks good to me now, +1 to kick off a voting thread. > > Best, > Kurt > > > On Fri, Oct 25, 2019 at 8:46 PM Danny Chan <yuzhao....@gmail.com> wrote: > > > Thanks, I have removed the contents about the “STORED” keyword, we may > > introduce that in the future if there is requests. > > > > Also thanks all the reviewers for the design doc, I have resolved all the > > questions/suggestions in the doc at this time. > > > > I will kick off a voting thread shortly as there were no comments in this > > thread so far, so I would assume there are no objections :) > > > > Best, > > Danny Chan > > 在 2019年10月24日 +0800 PM5:11，Kurt Young <ykt...@gmail.com>，写道： > > > +1 to move to a future section. By deleting it I mean remove from > > > the content describing the current processing procedure. > > > > > > Best, > > > Kurt > > > > > > > > > On Thu, Oct 24, 2019 at 5:01 PM Timo Walther <twal...@apache.org> > wrote: > > > > > > > Having an MVP and a limited scope sounds good to me. But I would not > > > > remove the STORED keyword entirely from the document. > > > > > > > > It shows that we have a long-term vision. Instead of deleting this > > > > content, I would move it to a Outlook/Future Work section. > > > > > > > > Regards, > > > > Timo > > > > > > > > > > > > On 24.10.19 10:55, Jark Wu wrote: > > > > > +1 to remove “STORED” related content. We can add them when user > > > > requires. > > > > > Others looks good to me in general. > > > > > > > > > > Thanks, > > > > > Jark > > > > > > > > > > > > > > > > 在 2019年10月24日，14:58，Kurt Young <ykt...@gmail.com> 写道： > > > > > > > > > > > > Hi Danny, > > > > > > > > > > > > Thanks for preparing this design document. IMO It's a very useful > > > > > > feature, especially combined with time attribute support to > specify > > > > > > watermark in DDL. > > > > > > > > > > > > The design doc looks quite good, but I would suggest to reduce > the > > > > > > scope of the first version. Like we don't have to support > "STORED" > > > > > > in the first MVP version, and you can also delete related content > > in > > > > > > document to make it more clean and easier to understand. > > > > > > > > > > > > Best, > > > > > > Kurt > > > > > > > > > > > > > > > > > > On Tue, Sep 17, 2019 at 9:18 PM Qi Luo <luoqi...@gmail.com> > wrote: > > > > > > > > > > > > > Fantastic! We're also very interested in this feature. > > > > > > > > > > > > > > +Boxiu > > > > > > > > > > > > > > On Tue, Sep 17, 2019 at 11:31 AM Danny Chan < > > yuzhao....@gmail.com> > > > > wrote: > > > > > > > > > > > > > > > In umbrella task FLINK-10232 we have introduced CREATE TABLE > > grammar > > > > in > > > > > > > > our new module flink-sql-parser. And we proposed to use > > computed > > > > column > > > > > > > to > > > > > > > > describe the time attribute of process time in the design doc > > FLINK > > > > SQL > > > > > > > > DDL, so user may create a table with process time attribute > as > > > > follows: > > > > > > > > create table T1( > > > > > > > > a int, > > > > > > > > b bigint, > > > > > > > > c varchar, > > > > > > > > d as PROCTIME, > > > > > > > > ) with ( > > > > > > > > 'k1' = 'v1', > > > > > > > > 'k2' = 'v2' > > > > > > > > ); > > > > > > > > > > > > > > > > The column d would be a process time attribute for table T1. > > > > > > > > > > > > > > > > Besides that, computed columns have several other use cases, > > such as > > > > > > > > these [2]: > > > > > > > > > > > > > > > > > > > > > > > > • Virtual generated columns can be used as a way to simplify > > and unify > > > > > > > > queries. A complicated condition can be defined as a > generated > > column > > > > and > > > > > > > > referred to from multiple queries on the table to ensure that > > all of > > > > them > > > > > > > > use exactly the same condition. > > > > > > > > • Stored generated columns can be used as a materialized > cache > > for > > > > > > > > complicated conditions that are costly to calculate on the > fly. > > > > > > > > • Generated columns can simulate functional indexes: Use a > > generated > > > > > > > > column to define a functional expression and index it. This > > can be > > > > useful > > > > > > > > for working with columns of types that cannot be indexed > > directly, > > > > such > > > > > > > as > > > > > > > > JSON columns. > > > > > > > > • For stored generated columns, the disadvantage of this > > approach is > > > > that > > > > > > > > values are stored twice; once as the value of the generated > > column and > > > > > > > once > > > > > > > > in the index. > > > > > > > > • If a generated column is indexed, the optimizer recognizes > > query > > > > > > > > expressions that match the column definition and uses indexes > > from the > > > > > > > > column as appropriate during query execution(Not supported > > yet). > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Computed columns are introduced in SQL-SERVER-2016 [1], > > MYSQL-5.6 [2] > > > > and > > > > > > > > ORACLE-11g [3]. > > > > > > > > > > > > > > > > This is the design doc: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://docs.google.com/document/d/110TseRtTCphxETPY7uhiHpu-dph3NEesh3mYKtJ7QOY/edit?usp=sharing > > > > > > > > > > > > > > > > Any suggestions are appreciated, thanks. > > > > > > > > > > > > > > > > [1] > > > > > > > > > > > > > > > > > > > > > > https://docs.microsoft.com/en-us/sql/relational-databases/tables/specify-computed-columns-in-a-table?view=sql-server-2016 > > > > > > > > [2] > > > > > > > > > > > > > > > > > > > > > > https://dev.mysql.com/doc/refman/5.7/en/create-table-generated-columns.html > > > > > > > > [3] > https://oracle-base.com/articles/11g/virtual-columns-11gr1 > > > > > > > > > > > > > > > > Best, > > > > > > > > Danny Chan > > > > > > > > > > > > > > > > > > > > > > > > > >
