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From Vitalii Diravka <vitalii.dira...@gmail.com>
Subject Re: Implement "DROP TABLE IIF EXISTS" statement
Date Fri, 01 Jul 2016 18:07:50 GMT
Agree with the last decision to use "IF EXISTS" statement and `if` udf with
backticks.
It is acceptable option.

Thank you for valuable advices.

Kind regards
Vitalii

2016-06-30 17:22 GMT+00:00 John Omernik <john@omernik.com>:

> I agree with Julian. If we can backtick quote Hive's if and have an option
> for Hive users, it would be nice. But Hive made a mess, and there is
> precedent for IF.  This makes from a cluster administration perspective,
> and even being a Hive user, as long as I had an option (with backticks) to
> allow me to move forward, I'd understand and accept the required changes.
>
> John
>
>
> On Thu, Jun 30, 2016 at 12:00 PM, Julian Hyde <jhyde@apache.org> wrote:
>
> > Even though it’s not standard, several other databases have DROP TABLE …
> > IF EXISTS (MySQL [1]; Postgres [2] and SQL Server 2016 [3] put the “IF
> > EXISTS” before the table name). I know there are problems with the IF
> > keyword clashing with the Hive “IF” function, but I think it would be
> crazy
> > to do “IIF EXISTS”.
> >
> > I’d block Hive’s “IF” function, frankly. They screwed up. No need to
> > propagate their mess into Drill.
> >
> > Julian
> >
> > [1] http://dev.mysql.com/doc/refman/5.7/en/drop-table.html <
> > http://dev.mysql.com/doc/refman/5.7/en/drop-table.html>
> >
> > [2] https://www.postgresql.org/docs/8.2/static/sql-droptable.html <
> > https://www.postgresql.org/docs/8.2/static/sql-droptable.html>
> >
> > [3]
> >
> https://blogs.msdn.microsoft.com/sqlserverstorageengine/2015/11/03/drop-if-exists-new-thing-in-sql-server-2016/
> > <
> >
> https://blogs.msdn.microsoft.com/sqlserverstorageengine/2015/11/03/drop-if-exists-new-thing-in-sql-server-2016/
> > >
> >
> > > On Jun 30, 2016, at 5:06 AM, Khurram Faraaz <kfaraaz@maprtech.com>
> > wrote:
> > >
> > > I looked at the SQL standard and I did not find that IF EXISTS is a
> part
> > of
> > > DROP TABLE syntax, please see below.
> > >
> > > INTERNATIONAL STANDARD
> > > ISO/IEC 9075-2
> > > Fourth edition 2011-12-15
> > >
> > >
> > > Format
> > > <drop table statement> ::=
> > >  DROP TABLE <table name> <drop behavior>
> > >
> > >  <drop behavior> ::=
> > >    CASCADE
> > >  | RESTRICT
> > >
> > > On Thu, Jun 30, 2016 at 3:44 PM, Arina Yelchiyeva <
> > > arina.yelchiyeva@gmail.com> wrote:
> > >
> > >> To sum up currently we are facing two options:
> > >>
> > >> 1. Add IF as keyword.
> > >> Pros:
> > >> DROP TABLE / VIEW IF EXISTS will work
> > >> Cons:
> > >> if function (loaded from Hive) will stop working. In this case users
> > will
> > >> have two options:
> > >> a) surround if with backticks (ex: select `if`(condition,option1,
> > option2)
> > >> from table)
> > >> b) replace if function with case statement
> > >>
> > >> 2. Use IIF instead of IF
> > >> Pros:
> > >> if function will work, no backward compatibility issues.
> > >> Cons:
> > >> uncommon syntax for IF EXISTS statement
> > >>
> > >> So far none of this options seems to be ideal.
> > >>
> > >> Kind regards
> > >> Arina
> > >>
> > >>
> > >> On Wed, Jun 29, 2016 at 8:56 PM Paul Rogers <progers@maprtech.com>
> > wrote:
> > >>
> > >>> Hi Vitalii,
> > >>>
> > >>> This will be a nice improvement. Your question about “IIF” vs.
“IF”
> is
> > in
> > >>> the context of one small enhancement. But, it raises a larger
> question
> > >>> (which is beyond the scope of your project, but is worth discussing
> > >> anyway.)
> > >>>
> > >>> That larger issue is that we really should modify the Drill SQL
> parser
> > to
> > >>> better handle keywords vs. identifiers. That is, the following
> > >>> “pathological” statement should be valid:
> > >>>
> > >>> SELECT select, from FROM from, where WHERE from.select = where.from;
> > >>>
> > >>> This seems very confusing to us humans. But, to the SQL grammar the
> > above
> > >>> is unambiguous. SQL syntax determines where a keyword is valid. All
> > other
> > >>> uses of that keyword can easily be interpreted as an identifier.
> > Further,
> > >>> the location of the identifier determines whether to interpreted it
> as
> > a
> > >>> column, table, schema, function, etc. For example, a keyword will
> never
> > >>> appear in a select list, from list or where expression. Technically,
> we
> > >>> could introduce distinct name spaces for keywords, columns, tables,
> > >>> functions and so on.
> > >>>
> > >>> Without this change we run two risks:
> > >>>
> > >>> 1. We can’t use proper SQL syntax when we need it (as in your
> project.)
> > >>> 2. We risk breaking queries when we add new keywords (as in the
> dynamic
> > >>> UDF project.)
> > >>>
> > >>> This is not a new idea. Informix made this very change to their
> parser,
> > >>> for similar reasons — and did it back in the late ‘80s using C
and
> YACC
> > >>> (for you old timers.)
> > >>>
> > >>> I’m not familiar with the Calcite parser. Anyone know what would
be
> > >>> involved in making this change so Vitalii can use proper SQL syntax?
> > >>>
> > >>> - Paul
> > >>>
> > >>>
> > >>>> On Jun 29, 2016, at 10:15 AM, Vitalii Diravka <
> > >> vitalii.diravka@gmail.com>
> > >>> wrote:
> > >>>>
> > >>>> Hi all!
> > >>>>
> > >>>> I'm going to implement "DROP TABLE IIF EXISTS" and "DROP VIEW IIF
> > >> EXISTS"
> > >>>> statements in Drill (DRILL-4673
> > >>>> <https://issues.apache.org/jira/browse/DRILL-4673>).
> > >>>> The reason of using "IIF" is inability of adding "IF" keyword to
> > >>>> non-reserved words list (due to SQL:2011 standard which calcite
> parser
> > >>>> uses). Adding of "IF" to reserved words list leads to not working
> hive
> > >>> "IF"
> > >>>> UDF.
> > >>>>
> > >>>> I'm interested are there any concerns with using "IIF" ?
> > >>>>
> > >>>> Kind regards
> > >>>> Vitalii
> > >>>
> > >>>
> > >>
> >
> >
>

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