code: protected void addToSelectList(
  		List<SqlNode> list,
  		Set<String> aliases,
  		List<Map.Entry<String, RelDataType>> fieldList,
  		SqlNode exp,
  		SqlValidatorScope scope,
  		final boolean includeSystemVars) {
  		String alias = SqlValidatorUtil.getAlias(exp, -1);
  		String uniqueAlias =
  			SqlValidatorUtil.uniquify(
  				alias, aliases, SqlValidatorUtil.EXPR_SUGGESTER);
  		if (!alias.equals(uniqueAlias)) {
  			exp = SqlValidatorUtil.addAlias(exp, uniqueAlias);
  		}
  		fieldList.add(Pair.of(uniqueAlias, deriveType(scope, exp)));
  		list.add(exp);
  	}
docs: Adds an expression to a select list, ensuring that its alias does not
  clash with any existing expressions on the list.