Function buildRelationAliases

src/backend/parser/parse_relation.c:1133–1195

* buildRelationAliases * Construct the eref column name list for a relation RTE. * This code is also used for function RTEs. * * tupdesc: the physical column information * alias: the user-supplied alias, or NULL if none * eref: the eref Alias to store column names in * * eref->colnames is filled in. Also, alias->colnames is rebuilt to insert * empty strings for any dropped columns, so

 * It is an error for there to be more aliases present than required.
 */
static void
buildRelationAliases(TupleDesc tupdesc, Alias *alias, Alias *eref)
{
	int			maxattrs = tupdesc->natts;
	List	   *aliaslist;
	ListCell   *aliaslc;
	int			numaliases;
	int			varattno;
	int			numdropped = 0;

	Assert(eref->colnames == NIL);

	if (alias)
	{
		aliaslist = alias->colnames;
		aliaslc = list_head(aliaslist);
		numaliases = list_length(aliaslist);
		/* We'll rebuild the alias colname list */
		alias->colnames = NIL;
	}
	else
	{
		aliaslist = NIL;
		aliaslc = NULL;
		numaliases = 0;
	}

	for (varattno = 0; varattno < maxattrs; varattno++)
	{
		Form_pg_attribute attr = TupleDescAttr(tupdesc, varattno);
		Value	   *attrname;

		if (attr->attisdropped)
		{
			/* Always insert an empty string for a dropped column */
			attrname = makeString(pstrdup(""));
			if (aliaslc)
				alias->colnames = lappend(alias->colnames, attrname);
			numdropped++;
		}
		else if (aliaslc)
		{
			/* Use the next user-supplied alias */
			attrname = (Value *) lfirst(aliaslc);
			aliaslc = lnext(aliaslist, aliaslc);
			alias->colnames = lappend(alias->colnames, attrname);
		}
		else
		{
			attrname = makeString(pstrdup(NameStr(attr->attname)));
			/* we're done with the alias if any */
		}

		eref->colnames = lappend(eref->colnames, attrname);
	}

	/* Too many user-supplied aliases? */
	if (aliaslc)