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From Mamta Satoor <msat...@gmail.com>
Subject Re: [PATCH] (DERBY-582) Dynamic parameter should be allowed to be the operand of unary operator "-". Derby throws exception 42X36: The '-' operator is not allowed to take a ? parameter as an operand."
Date Thu, 29 Sep 2005 05:57:37 GMT
Hi Jeff,
 I agree with your and Dan's point about possible precision loss. I am
trying to find a way where rather than hard coding the -?/+? to Double, try
to get it's datatype from the context where it is used.
 For instance, say there is a table t1 with columns c11 as decimal(2,1) and
c12 as int, Then for following sql
select * from t1 where c11 = -? and c12 = +?
The first parameter should be bound to decimal and the second parameter
should be bound to int.
 Looking at the code for UnaryOperatorNode/UnaryArithmeticOperatorNode, it
seems like it is going to be tricky to pass on the datatype of the left
operand in above example to UnaryArithmeticOperator.
 Some info about current code flow for the specific example above and one
possible generic solution
BinaryOperatorNode.bindExpression calls bindExpression on the left operand
(line 307 in the code) and then on the right operand
(UnaryArithmeticOperatorNode). The right operand at this point doesn't know
what type it should be bound to. In my preliminary changes, I am making the
bindExpression no-op for UnaryArithmeticOperatorNode if it has a parameter
operand which is not bound to any type yet. Later in
BinaryOperatorNode.bindExpression (line 335), the right operand gets bound
to the same type as the left operand through the setDescriptor call, which
is what we want. Once we have the correct type, we now want to run
bindExpression on the UnaryArithmeticOperator. In my changes, I am
overriding the setDescriptor method in UnaryArithmeticOperatorNode and
having it call the bindExpression after it sets the type of the parameter to
the left operand's type. Calling bindExpression will run all the bind time
rules that should be run on a UnaryArithmeticOperatorNode. I haven't run
enough tests to know if this is full proof but looking from outside, does
anyone think there is a better solution than this? Even if my changes work
fine, they seem more like a hack because during the actual bindExpression
call, I am treating it as a no-op and then forcing the bindExpression later
when UnaryArithmeticOperator does get the correct type. Any feedback from
the community on this will be great.
 thanks,
Mamta

 On 9/28/05, Jeffrey Lichtman <swazoo@rcn.com> wrote:
>
>
> >I have a simple patch to allow dynamic parameters for unary minus
> >and plus. The parameter will be bound to DOUBLE. The patch is
> >attached to JIRA. Can a commiter please commit it if everything
> >looks good? I have run all the tests and no new failures. Have also
> >added a test for this.
>
> I'm not convinced this is a good idea.
>
> The SQL standard limits the use of parameters to those places where
> their types can be determined unambiguously, for example, in an
> insert or update list, or as an argument to the CAST function. I
> don't know of any general way to figure out what the type of a
> parameter "should" be in other places, especially for overloaded
> functions and operators like - (both unary and binary).
>
> What will happen if Cloudscape binds a parameter to a double, and the
> user tries to use it with a fixed-point type like decimal? It's
> likely there will be a loss of precision, and the user won't get what
> he expects.
>
> If the user wants to use a parameter with unary minus, I suggest the
> use of the cast function to make the type unambiguous:
>
> - (cast ? as <type>)
>
>
> - Jeff Lichtman
> swazoo@rcn.com
> Check out Swazoo Koolak's Web Jukebox at
> http://swazoo.com/
>
>

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