Question

Having a table with the following fields:

Order,Group,Sequence

it is required that all orders in a given group form a continuous sequence. For example: 1,2,3,4 or 4,5,6,7. How can I check using a single SQL query what orders do not comply with this rule? Thank you.

Example data:

Order   Group   Sequence
1   1   3
2   1   4
3   1   5
4   1   6
5   2   3
6   2   4
7   2   6

Expected result:
Order
5
6
7

Also accepted if the query returns only the group which has the wrong sequence, 2 for the example data.

Answer 1

Assuming that the sequences are generated and therefore cannot be duplicated:

SELECT group
 FROM theTable
 GROUP BY group
 HAVING MAX(Sequence) - MIN(Sequence) &lt> (COUNT(*) - 1);