Function ExecInitJunkFilter

src/backend/executor/execJunk.c:63–132

* ExecInitJunkFilter * * Initialize the Junk filter. * * The source targetlist is passed in. The output tuple descriptor is * built from the non-junk tlist entries. * An optional resultSlot can be passed as well; otherwise, we create one. * An optional execFilterJunkFunc can be passed as well; otherwise, we use ExecFilterJunk. */

 * An optional execFilterJunkFunc can be passed as well; otherwise, we use ExecFilterJunk.
 */
JunkFilter *
ExecInitJunkFilter(List *targetList, TupleTableSlot *slot,
				   ExecFilterJunkFunc execFilterJunkFunc)
{
	JunkFilter *junkfilter;
	TupleDesc	cleanTupType;
	int			cleanLength;
	AttrNumber *cleanMap;

	/*
	 * Compute the tuple descriptor for the cleaned tuple.
	 */
	cleanTupType = ExecCleanTypeFromTL(targetList);

	/*
	 * Use the given slot, or make a new slot if we weren't given one.
	 */
	if (slot)
		ExecSetSlotDescriptor(slot, cleanTupType);
	else
		slot = MakeSingleTupleTableSlot(cleanTupType, &TTSOpsVirtual);

	/*
	 * Now calculate the mapping between the original tuple's attributes and
	 * the "clean" tuple's attributes.
	 *
	 * The "map" is an array of "cleanLength" attribute numbers, i.e. one
	 * entry for every attribute of the "clean" tuple. The value of this entry
	 * is the attribute number of the corresponding attribute of the
	 * "original" tuple.  (Zero indicates a NULL output attribute, but we do
	 * not use that feature in this routine.)
	 */
	cleanLength = cleanTupType->natts;
	if (cleanLength > 0)
	{
		AttrNumber	cleanResno;
		ListCell   *t;

		cleanMap = (AttrNumber *) palloc(cleanLength * sizeof(AttrNumber));
		cleanResno = 0;
		foreach(t, targetList)
		{
			TargetEntry *tle = lfirst(t);

			if (!tle->resjunk)
			{
				cleanMap[cleanResno] = tle->resno;
				cleanResno++;
			}
		}
		Assert(cleanResno == cleanLength);
	}
	else
		cleanMap = NULL;

	/*
	 * Finally create and initialize the JunkFilter struct.
	 */