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Posted to derby-dev@db.apache.org by Nirmal Fernando <ni...@gmail.com> on 2010/04/18 09:37:11 UTC
Checking an Expressions
Hi All,
How can we check whether a particular ValueNode is an "expression" (eg: i*2) ?.
*Note: We can check "ValueNode instance of ColumnReference" to check
whether it is a column (eg: i).
Thanks.
--
Best Regards,
Nirmal
C.S.Nirmal J. Fernando
Department of Computer Science & Engineering,
Faculty of Engineering,
University of Moratuwa,
Sri Lanka.
Re: Checking an Expressions
Posted by Nirmal Fernando <ni...@gmail.com>.
Thanks Bryan for the very clear explanation, I think this will be very
useful to me.
On Sun, Apr 18, 2010 at 8:35 PM, Bryan Pendleton
<bp...@gmail.com> wrote:
> Nirmal Fernando wrote:
>>
>> How can we check whether a particular ValueNode is an "expression" (eg:
>> i*2) ?.
>>
>> *Note: We can check "ValueNode instance of ColumnReference" to check
>> whether it is a column (eg: i).
>
> I think that every ValueNode is an expression of some sort. Consider:
>
> select name from employee;
> select year_hired - 1900 from employee;
> select max(salary) from employee;
> select current_date from employee;
> select first_name || ' ' || last_name from employee;
>
> All of these will result in various ValueNode instances being constructed.
> Some are
> simple ColumnReference nodes. Others are more complex expressions.
>
> Unfortunately (or fortunately, depending on how you look at it), ValueNode
> is
> an extremely general-purpose class in Derby, and there are a large number
> of particular sub-classes of ValueNode that are of interest.
>
> It so happens that the case of "a simple direct reference to a column in
> this table"
> is extremely common, and has a number of optimizations that we perform, and
> so
> you see code in Derby that says
>
> if (expression instanceof ColumnReference)
>
> quite commonly. However, there are many sub-classes of ValueNode. Consider
> that these classes are just some of the *direct* sub-classes of ValueNode:
>
> BaseColumnNode.java:public class BaseColumnNode extends ValueNode
> BinaryListOperatorNode.java:public abstract class BinaryListOperatorNode
> extends ValueNode
> BinaryOperatorNode.java:public class BinaryOperatorNode extends ValueNode
> CastNode.java:public class CastNode extends ValueNode
> CoalesceFunctionNode.java:public class CoalesceFunctionNode extends
> ValueNode
> ColumnReference.java:public class ColumnReference extends ValueNode
> ConditionalNode.java:public class ConditionalNode extends ValueNode
> ConstantNode.java:abstract class ConstantNode extends ValueNode
> CurrentDatetimeOperatorNode.java:public class CurrentDatetimeOperatorNode
> extends ValueNode {
> CurrentRowLocationNode.java:public class CurrentRowLocationNode extends
> ValueNode
> DefaultNode.java:public class DefaultNode extends ValueNode
> GenerationClauseNode.java:public class GenerationClauseNode extends
> ValueNode
> JavaToSQLValueNode.java:public class JavaToSQLValueNode extends ValueNode
> NextSequenceNode.java:public class NextSequenceNode extends ValueNode {
> ParameterNode.java:public class ParameterNode extends ValueNode
> ResultColumn.java:public class ResultColumn extends ValueNode
> SpecialFunctionNode.java:public class SpecialFunctionNode extends ValueNode
> SubqueryNode.java:public class SubqueryNode extends ValueNode
> TernaryOperatorNode.java:public class TernaryOperatorNode extends ValueNode
> UnaryOperatorNode.java:public class UnaryOperatorNode extends ValueNode
> VirtualColumnNode.java:public class VirtualColumnNode extends ValueNode
>
> And many of these classes have further sub-classes of them.
>
> You might finding it helpful to use the parse-tree-printing support in Derby
> to dump
> out the parse tree from several sample queries and have a look at how the
> parse
> trees are put together.
>
> I think that you can use the ASTVisitor support that was added in DERBY-4415
> (https://issues.apache.org/jira/browse/DERBY-4415) and DERBY-791
> (https://issues.apache.org/jira/browse/DERBY-791) to view the parse trees.
>
> thanks,
>
> bryan
>
>
--
Best Regards,
Nirmal
C.S.Nirmal J. Fernando
Department of Computer Science & Engineering,
Faculty of Engineering,
University of Moratuwa,
Sri Lanka.
Re: Checking an Expressions
Posted by Bryan Pendleton <bp...@gmail.com>.
Nirmal Fernando wrote:
> How can we check whether a particular ValueNode is an "expression" (eg: i*2) ?.
>
> *Note: We can check "ValueNode instance of ColumnReference" to check
> whether it is a column (eg: i).
I think that every ValueNode is an expression of some sort. Consider:
select name from employee;
select year_hired - 1900 from employee;
select max(salary) from employee;
select current_date from employee;
select first_name || ' ' || last_name from employee;
All of these will result in various ValueNode instances being constructed. Some are
simple ColumnReference nodes. Others are more complex expressions.
Unfortunately (or fortunately, depending on how you look at it), ValueNode is
an extremely general-purpose class in Derby, and there are a large number
of particular sub-classes of ValueNode that are of interest.
It so happens that the case of "a simple direct reference to a column in this table"
is extremely common, and has a number of optimizations that we perform, and so
you see code in Derby that says
if (expression instanceof ColumnReference)
quite commonly. However, there are many sub-classes of ValueNode. Consider
that these classes are just some of the *direct* sub-classes of ValueNode:
BaseColumnNode.java:public class BaseColumnNode extends ValueNode
BinaryListOperatorNode.java:public abstract class BinaryListOperatorNode extends ValueNode
BinaryOperatorNode.java:public class BinaryOperatorNode extends ValueNode
CastNode.java:public class CastNode extends ValueNode
CoalesceFunctionNode.java:public class CoalesceFunctionNode extends ValueNode
ColumnReference.java:public class ColumnReference extends ValueNode
ConditionalNode.java:public class ConditionalNode extends ValueNode
ConstantNode.java:abstract class ConstantNode extends ValueNode
CurrentDatetimeOperatorNode.java:public class CurrentDatetimeOperatorNode extends ValueNode {
CurrentRowLocationNode.java:public class CurrentRowLocationNode extends ValueNode
DefaultNode.java:public class DefaultNode extends ValueNode
GenerationClauseNode.java:public class GenerationClauseNode extends ValueNode
JavaToSQLValueNode.java:public class JavaToSQLValueNode extends ValueNode
NextSequenceNode.java:public class NextSequenceNode extends ValueNode {
ParameterNode.java:public class ParameterNode extends ValueNode
ResultColumn.java:public class ResultColumn extends ValueNode
SpecialFunctionNode.java:public class SpecialFunctionNode extends ValueNode
SubqueryNode.java:public class SubqueryNode extends ValueNode
TernaryOperatorNode.java:public class TernaryOperatorNode extends ValueNode
UnaryOperatorNode.java:public class UnaryOperatorNode extends ValueNode
VirtualColumnNode.java:public class VirtualColumnNode extends ValueNode
And many of these classes have further sub-classes of them.
You might finding it helpful to use the parse-tree-printing support in Derby to dump
out the parse tree from several sample queries and have a look at how the parse
trees are put together.
I think that you can use the ASTVisitor support that was added in DERBY-4415
(https://issues.apache.org/jira/browse/DERBY-4415) and DERBY-791
(https://issues.apache.org/jira/browse/DERBY-791) to view the parse trees.
thanks,
bryan