Yeah Stamatis, I know that as I can see the github page for linq4j that
lots of task is in Backlog and Link-To-SQL Provider is one of them
But the intention of the project is to make java objects as Queryable talk
to DB.
Expressions and various Statement used in linq4j is to generate the
different constructs like where filter, join to talk the back-end systems
as Sql Queries.
But what about the normal While loop and If then else statements which is
not used in the Query-able objects .
Example could be below:
LOOP
SET heads = RAND() < 0.5;
IF heads THEN
SELECT 'Heads!';
SET heads_count = heads_count + 1;
ELSE
SELECT 'Tails!';
BREAK;
END IF;
END LOOP;
SELECT CONCAT(CAST(heads_count AS STRING), ' heads in a row');
How linq4j going to convert normal while and If then else java expressions
to sql query if they are not involved in computation of sql constructs like
in lambda expression of filter.
In one of the task in backlog I could see:
*In the prototype LINQ-to-SQL provider, write a simple rule to recognize a
select list and where clause and push them down to SQL.*
I believe it was never intended for procedural code right?
Thanks,
Ravi
On Wed, Apr 22, 2020 at 2:43 AM Stamatis Zampetakis <zabe...@gmail.com>
wrote:
> Hi Ravi,
>
> As Julian already mentioned, we are quite far from what you would like to
> achieve.
>
> Nevertheless, I would like to mention that you can model certain kind of
> loops and recursion using the RepeatUnion [1] and Spool [2] relational
> expressions. Note that these APIs are experimental.
>
> Moreover, if your end goal is to push the computation in a DBMS, I have to
> warn you that the code to translate these expressions back to SQL is not
> there yet.
>
> Best,
> Stamatis
>
> [1]
>
> https://github.com/apache/calcite/blob/master/core/src/main/java/org/apache/calcite/rel/core/RepeatUnion.java
> [2]
>
> https://github.com/apache/calcite/blob/master/core/src/main/java/org/apache/calcite/rel/core/Spool.java
>
> On Mon, Apr 20, 2020 at 8:08 PM Julian Hyde <jh...@apache.org> wrote:
>
> > Calcite relational expressions can represent SELECT, INSERT etc. but not
> > procedural code. It’s a direction we could consider going.
> >
> > RexProgram is the closest thing we currently have to procedural code in
> > the algebra - single assignment of variables, use of variables in
> > expressions assigning to other variables - but it is a long way short
> > because there are no loops.
> >
> > > On Apr 19, 2020, at 12:47 PM, Ravi Kapoor <kapoorrav...@gmail.com>
> > wrote:
> > >
> > > Hi Team,
> > >
> > > I have my use where I need to convert my dialect specific stored
> > procedure
> > > constructs like while loop, If then else to Rel expression
> > >
> > > Basically this can contain control flow statements like below
> > >
> > > DECLARE heads BOOL;
> > > DECLARE heads_count INT64 DEFAULT 0;
> > > LOOP
> > > SET heads = RAND() < 0.5;
> > > IF heads THEN
> > > SELECT 'Heads!';
> > > SET heads_count = heads_count + 1;
> > > ELSE
> > > SELECT 'Tails!';
> > > BREAK;
> > > END IF;
> > > END LOOP;
> > > SELECT CONCAT(CAST(heads_count AS STRING), ' heads in a row');
> > >
> > >
> > > I can create a Java AST model from the linq4j provided by calcite
> however
> > > this is only going to generate Java Result and I believe its only used
> by
> > > the calcite for relational expressions of enumerable calling convention
> > > which is used by adapters which does not support core relational
> > operations
> > > right?
> > >
> > > Is there a way I can convert the stored proc constructs into some
> > canonical
> > > form like Rel Tree and back to Stored proc of target dialect.
> > > --
> > >
> > > Thanks,
> > > Ravi
> >
> >
>
--
Thanks,
Ravi Kapoor
+91-9818764564
kapoorrav...@gmail.com
