How do I query for fields that have AT LEAST a given range?

Question

Say I have a table of the form:

+-----+-------+
| Key | Value |
+-----+-------+
| A   |     1 |
| A   |     3 |
| A   |     4 |
| B   |     2 |
| B   |     3 |
| C   |     3 |
| C   |     4 |
| C   |     5 |
+-----+-------+

I want to be able to return all of the keys that have at least a given range.

For example:

A query for a Value range of 2 would return A, B, C
A query for a Value range of 3 would return A, C
A query for a Value range of 4 would return A

Can this be done with SQL (specifically SQLite)? If so, how?

Answer 1

To find those with a "range" of at least 4 for example

SELECT "Key"
FROM   YourTable
GROUP  BY "Key"
HAVING (1 + MAX("Value") - MIN ("Value")) >= 4; 

Obviously alter the 4 as appropriate for the other cases.

SQL Fiddle