Re: ExecEvalVar does not have appropriate ExprState? - Mailing list pgsql-hackers

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