Re: What would AggrefExprState nodes' args contain?

The args in AggrefExprState, are used in the functions ExecAgg, ExecInitAgg and their minions to evaluate the
aggregates.The ExecEvalAggref() merely retrieves the results of aggregation calculated during ExecAgg.<br /><br /><div
class="gmail_quote">On Tue, Apr 26, 2011 at 12:04 PM, Vaibhav Kaushal <span dir="ltr"><<a
href="mailto:[email protected]">[email protected]</a>></span>wrote:<br /><blockquote
class="gmail_quote"style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
Helloall,<br /><br />While examining the executor, I was wondering what the *args part of AggrefExprState nodes
contain.I found that the Aggref (Expr)'s  args list is a list of TargetEntry nodes. But the state node's args is
initializedin ExecInitExpr as:<br /><br />astate->args = (List *) ExecInitExpr((Expr *) aggref->args,<br />   
                                                    parent);<br /><br />This would mean that the args is actually a
ExprStatenode list with one single item (the ExprState node / tree). I believe it potentially contains the execution
treeto determine the state / value of the aggref (sub)expression. But then in the ExecEvalAggref function I do not see
theargs coming into picture at all! I am also unable to find a call to some function for executing the state node
createdin the args list. Also, no value is being extracted from that node! Why is it so? <br /><br />For quick
referenceI am adding the function (may be you don't need it but still... its a small one):<br /><br />/*
----------------------------------------------------------------<br/> *        ExecEvalAggref<br /> *<br />  *       
Returnsa Datum whose value is the value of the precomputed<br /> *        aggregate found in the given expression
context.<br/> * ----------------------------------------------------------------<br /> */<br />static Datum<br />
ExecEvalAggref(AggrefExprState*aggref, ExprContext *econtext,<br />               bool *isNull, ExprDoneCond
*isDone)<br/>{<br />   if (isDone)<br />        *isDone = ExprSingleResult;<br /><br />    if
(econtext->ecxt_aggvalues== NULL)        /* safety check */<br />         elog(ERROR, "no aggregates in this
expressioncontext");<br /><br />    *isNull = econtext->ecxt_aggnulls[aggref->aggno];<br />    return
econtext->ecxt_aggvalues[aggref->aggno];<br/>}<br /><br /><br />What is the use of args in AggrefExprState node
here?Is it there just for some historical reason?<br /><br />Regards,<br /><font color="#888888">Vaibhav <br
/></font></blockquote></div><br/><br clear="all" /><br />-- <br />Best Wishes,<br />Ashutosh Bapat<br />EntepriseDB
Corporation<br/>The Enterprise Postgres Company<br /><br />