[QA] Test ORDER BY/LIMIT combinations

Exercise a query of the following form:

```sql
SELECT field FROM table ORDER BY field1 [DESC|ASC] [NULLS FIRST|NULLS LAST] LIMIT N
```

We vary
- [x] number of identical elements in collection
- [x] DESC/ASC
- [x] NULLS FIRST/NULLS LAST/UNSPECIFIED
- [x] LIMIT VALUE (1, 2, 3)

We should compare with MySQL, since our default comparison for NULL is smaller than other values.