Function build_pertrans_for_aggref

src/backend/executor/nodeAgg.c:4337–4642

* Build the state needed to calculate a state value for an aggregate. * * This initializes all the fields in 'pertrans'. 'aggref' is the aggregate * to initialize the state for. 'aggtransfn', 'aggtranstype', and the rest * of the arguments could be calculated from 'aggref', but the caller has * calculated them already, so might as well pass them. */

 * calculated them already, so might as well pass them.
 */
static void
build_pertrans_for_aggref(AggStatePerTrans pertrans,
						  AggState *aggstate, EState *estate,
						  Aggref *aggref,
						  Oid aggtransfn, Oid aggtranstype,
						  Oid aggserialfn, Oid aggdeserialfn,
						  Datum initValue, bool initValueIsNull,
						  Oid *inputTypes, int numArguments)
{
	int			numGroupingSets = Max(aggstate->maxsets, 1);
	Expr	   *serialfnexpr = NULL;
	Expr	   *deserialfnexpr = NULL;
	ListCell   *lc;
	int			numInputs;
	int			numDirectArgs;
	List	   *sortlist;
	int			numSortCols;
	int			numDistinctCols;
	int			i;

	/* Begin filling in the pertrans data */
	pertrans->aggref = aggref;
	pertrans->aggshared = false;
	pertrans->aggCollation = aggref->inputcollid;
	pertrans->transfn_oid = aggtransfn;
	pertrans->serialfn_oid = aggserialfn;
	pertrans->deserialfn_oid = aggdeserialfn;
	pertrans->initValue = initValue;
	pertrans->initValueIsNull = initValueIsNull;

	/* Count the "direct" arguments, if any */
	numDirectArgs = list_length(aggref->aggdirectargs);

	/* Count the number of aggregated input columns */
	pertrans->numInputs = numInputs = list_length(aggref->args);

	pertrans->aggtranstype = aggtranstype;

	/*
	 * When combining states, we have no use at all for the aggregate
	 * function's transfn. Instead we use the combinefn.  In this case, the
	 * transfn and transfn_oid fields of pertrans refer to the combine
	 * function rather than the transition function.
	 */
	if (DO_AGGSPLIT_COMBINE(pertrans->aggref->aggsplit))
	{
		Expr	   *combinefnexpr;
		size_t		numTransArgs;

		/*
		 * When combining there's only one input, the to-be-combined added
		 * transition value from below (this node's transition value is
		 * counted separately).
		 */
		pertrans->numTransInputs = 1;

		/* account for the current transition state */
		numTransArgs = pertrans->numTransInputs + 1;