Thanks Dawid for starting this discussion.
I like the "LIKE".
1.For "INHERITS", I think this is a good feature too, yes, ALTER TABLE will
propagate any changes in column data definitions and check constraints down
the inheritance hierarchy. A inherits B, A and B share every things, they
have the same kafka topic. If modify schema of B, this means underlying
kafka topic schema changed, so I think it is good to modify A too. If this
for "ConfluentSchemaRegistryCatalog" mention by Jark, I think sometimes
this is just we want.
But "LIKE" also very useful for many cases.
2.For LIKE statement in schema, I know two kinds of like syntax, one is
MySQL/hive/sqlserver, the other is PostgreSQL. I prefer former:
- In the FLIP, there is "OVERWRITING OPTIONS", this will overwrite
properties in "with"? This looks weird, because "LIKE" is in schema, but it
can affect outside properties.
Best,
Jingsong Lee
On Wed, Mar 4, 2020 at 2:05 PM Dawid Wysakowicz <dwysakow...@apache.org>
wrote:
> Hi Jark,
> I did investigate the INHERITS clause, but it has a semantic that in my
> opinion we definitely don't want to support. INHERITS creates a new table
> with a "link" to the original table. Therefore if you e.g change the schema
> of the original table it's also reflected in the child table. It's also
> possible for tables like A inherits B query them like Select * from only A,
> by default it returns results from both tables. I am pretty sure it's not
> what we're looking for.
>
> PostgreSQL implements both the LIKE clause and INHERITS. I am open for
> discussion if we should support multiple LIKE statements or not. Standard
> also allows declaring the clause after the schema part. We can also do it.
> Nevertheless I think including multiple tables might be useful, e.g. when
> you want to union two tables and output to the same Kafka cluster and just
> change the target topic. I know it's not a very common use case but it's
> not a big effort to support it.
>
> Let me know what you think.
>
> Best,
> Dawid
>
> On Wed, 4 Mar 2020, 04:55 Jark Wu, <imj...@gmail.com> wrote:
>
> > Hi Dawid,
> >
> > Thanks for starting this discussion. I like the idea.
> > Once we support more intergrated catalogs,
> > e.g. ConfluentSchemaRegistryCatalog, this problem will be more urgent.
> > Because it's very common to adjust existing tables in catalog slightly.
> >
> > My initial thought was introducing INHERITS keyword, which is also
> > supported in PostgreSQL [1].
> > This is also similar to the functionality of Hive CREATE TABLE LIKE [2].
> >
> > CREATE TEMPORARY TABLE MyTable (WATERMARK FOR ts) INHERITS
> > cat.db.KafkoTopic
> > CREATE TEMPORARY TABLE MyTable (WATERMARK FOR ts) INHERITS
> > cat.db.KafkoTopic WITH ('k' = 'v')
> >
> > The INHERITS can inherit an existing table with all columns, watermark,
> and
> > properties, but the properties and watermark and be overwrited
> explicitly.
> >
> > The reason I prefer INHERITS rather than LIKE is the keyword position. We
> > are copying an existing table definition including the properties.
> > However, LIKE appears in the schema part, it sounds like copying
> properties
> > into schema part of DDL.
> >
> > Besides of that, I'm not sure whether the use case stands "merging two
> > tables into a single one with a different connector".
> > From my understanding, most use cases are just slightly adjusting on an
> > existing catalog table with new properties or watermarks.
> > Do we really need to merge two table definitions into a single one? For
> > example, is it possible to merge a Kafka table definition and
> > a Filesystem table definition into a new Kafka table, and the new Kafka
> > table exactly matches the underlying physical data format?
> >
> > Best,
> > Jark
> >
> > [1]: https://www.postgresql.org/docs/9.5/sql-createtable.html
> > [2]:
> >
> >
> https://cwiki.apache.org/confluence/display/Hive/LanguageManual+DDL#LanguageManualDDL-CreateTableLike
> >
> >
> > On Tue, 3 Mar 2020 at 21:12, Dawid Wysakowicz <dwysakow...@apache.org>
> > wrote:
> >
> > > Hi devs,
> > >
> > > I wanted to bring another improvement proposal up for a discussion.
> Often
> > > users need to adjust existing tables slightly. This is especially
> useful
> > > when users need to enhance a table created from an external tool (e.g.
> > > HIVE) with Flink's specific information such as e.g watermarks. It can
> > also
> > > be a useful tool for ETL processes, e.g. merging two tables into a
> single
> > > one with a different connector. My suggestion would be to support an
> > > optional *Feature T171, “LIKE clause in table definition” *of SQL
> > > standard 2008.
> > >
> > > You can see the description of the proposal here:
> > >
> >
> https://cwiki.apache.org/confluence/display/FLINK/FLIP-110%3A+Support+LIKE+clause+in+CREATE+TABLE
> > >
> > > Looking forward for your comments.
> > >
> > > Best,
> > >
> > > Dawid
> > >
> >
>
--
Best, Jingsong Lee
