Function ExecBuildUpdateProjection

src/backend/executor/execExpr.c:524–744

* ExecBuildUpdateProjection * * Build a ProjectionInfo node for constructing a new tuple during UPDATE. * The projection will be executed in the given econtext and the result will * be stored into the given tuple slot. (Caller must have ensured that tuple * slot has a descriptor matching the target rel!) * * When evalTargetList is false, targetList contains the UPDATE ... SET * expressio

 * ExecCheckPlanOutput, so we must do our safety checks here.
 */
ProjectionInfo *
ExecBuildUpdateProjection(List *targetList,
						  bool evalTargetList,
						  List *targetColnos,
						  TupleDesc relDesc,
						  ExprContext *econtext,
						  TupleTableSlot *slot,
						  PlanState *parent)
{
	ProjectionInfo *projInfo = makeNode(ProjectionInfo);
	ExprState  *state;
	int			nAssignableCols;
	bool		sawJunk;
	Bitmapset  *assignedCols;
	LastAttnumInfo deform = {0, 0, 0};
	ExprEvalStep scratch = {0};
	int			outerattnum;
	ListCell   *lc,
			   *lc2;

	projInfo->pi_exprContext = econtext;
	/* We embed ExprState into ProjectionInfo instead of doing extra palloc */
	projInfo->pi_state.tag = T_ExprState;
	state = &projInfo->pi_state;
	if (evalTargetList)
		state->expr = (Expr *) targetList;
	else
		state->expr = NULL;		/* not used */
	state->parent = parent;
	state->ext_params = NULL;

	state->resultslot = slot;

	/*
	 * Examine the targetList to see how many non-junk columns there are, and
	 * to verify that the non-junk columns come before the junk ones.
	 */
	nAssignableCols = 0;
	sawJunk = false;
	foreach(lc, targetList)
	{
		TargetEntry *tle = lfirst_node(TargetEntry, lc);

		if (tle->resjunk)
			sawJunk = true;
		else
		{
			if (sawJunk)
				elog(ERROR, "subplan target list is out of order");
			nAssignableCols++;
		}
	}

	/* We should have one targetColnos entry per non-junk column */
	if (nAssignableCols != list_length(targetColnos))
		elog(ERROR, "targetColnos does not match subplan target list");

	/*