1 - порядковый номер в списке полей после select.
Вообщем конструкция эквивалентна
SELECT id FROM table GROUP BY id

Выкиньте ваш справочник.
Вот обычный фоксовый хелп

GROUP BY GroupColumn [, GroupColumn ...]
Groups rows in the query based on values in one or more columns. GroupColumn can be the name of a regular table field, a field that includes an SQL field function, or a numeric expression indicating the location of the column in the result table. The leftmost column number is 1.

ORDER BY Order_Item [ASC | DESC]
Sorts the query results based on the data in one or more columns. Each Order_Item must correspond to a column in the query results and can be one of the following:
A field in a FROM table that is also a Select_Item in the main SELECT clause (not a subquery).
A numeric expression indicating the location of the column in the result table. The leftmost column is number 1.