Обсуждение: ExecEvalVar does not have appropriate ExprState?

Hi,

I see the ExecInitExpr says something like this:
------------
case T_Var:state = (ExprState *) makeNode(ExprState);state->evalfunc = ExecEvalVar;
---------------


But the ExecEvalVar function definition says:

------------------------
Var           *variable = (Var *) exprstate->expr;TupleTableSlot *slot;AttrNumber    attnum;
if (isDone)    *isDone = ExprSingleResult;
/* Get the input slot and attribute number we want */switch (variable->varno){    case INNER:                /* get the
tuplefrom the inner node */
 
-------------------------


Since ExprState -> expr in its final form would finally contain only:

NodeTag        type;

I think that the pointer being cast in the ExecEvalVar is actually
already a form of Var which is passed around as Expr for sake of
function call. 

So, was the node in the Expr tree for the corresponding ExprState node
of the ExprState tree actually a 'Var'? I think without this being the
reality, the function ExecEvalVar would crash! In my belief, the similar
fact would stand for a few other nodes, notably Const, Param,
CoerceToDomain and CaseTest.

Also, I have tried, but failed to fidn the exact place where the Expr
tree is created. Just pointing me to the file / function which does this
would be of great help. 

Kindly correct me if I am wrong.

Regards,
Vaibhav 

On 28.03.2011 10:02, Vaibhav Kaushal wrote:
> Hi,
>
> I see the ExecInitExpr says something like this:
> ------------
> case T_Var:
>     state = (ExprState *) makeNode(ExprState);
>     state->evalfunc = ExecEvalVar;
> ---------------
>
>
> But the ExecEvalVar function definition says:
>
> ------------------------
> Var           *variable = (Var *) exprstate->expr;
>     TupleTableSlot *slot;
>     AttrNumber    attnum;
>
>     if (isDone)
>         *isDone = ExprSingleResult;
>
>     /* Get the input slot and attribute number we want */
>     switch (variable->varno)
>     {
>         case INNER:                /* get the tuple from the inner node */
> -------------------------
>
>
> Since ExprState ->  expr in its final form would finally contain only:
>
> NodeTag        type;
>
> I think that the pointer being cast in the ExecEvalVar is actually
> already a form of Var which is passed around as Expr for sake of
> function call.

Right, exprstate->expr is a Var in ExecEvalVar.

> So, was the node in the Expr tree for the corresponding ExprState node
> of the ExprState tree actually a 'Var'?

Yes.

> Also, I have tried, but failed to fidn the exact place where the Expr
> tree is created. Just pointing me to the file / function which does this
> would be of great help.

A raw expression tree is created in the grammar, 
src/backend/parser/gram.y. It is then transformed in parse analysis 
phase to the form the planner accepts, in transformExpr(). The planner 
can do some further transformations, like replacing immutable function 
calls with Consts.

--   Heikki Linnakangas  EnterpriseDB   http://www.enterprisedb.com

Thanks for the confirmation. I am happy to have understood some basics of PG.

Also, I think the similar stands for the Const, Param,
CoerceToDomain and CaseTest nodes, right? They too cast the pointer to another type.

Thanks for the help Heikki. (I could better call you HL, if you dont mind :P )

Regards,
Vaibhav

On 28.03.2011 10:44, Vaibhav Kaushal wrote:
> Also, I think the similar stands for the Const, Param,
> CoerceToDomain and CaseTest nodes, right? They too cast the pointer to
> another type.

Yep.

--   Heikki Linnakangas  EnterpriseDB   http://www.enterprisedb.com