True, but I doubt that's what the OP meant to get.
If it is, his original query relies on a special quirk of SQLite that is not guaranteed to work the same in future, and will not work in any other SQL engine.
If it *IS* the case, he is better off with:
```
WITH M(x, y, miny, maxy) AS (
SELECT x, y,
min(y) OVER (PARTITION BY (X/10)),
max(y) OVER (PARTITION BY (X/10))
FROM foo
)
SELECT x, y FROM M WHERE y = miny
UNION
SELECT x, y FROM M WHERE y = maxy
;
```
And there are no shortcuts to make that happen in a single loop I think. Perhaps persisting the subquery/CTE would be slightly faster?