Question

I need to write a query that selects a minimum value and it’s second most minimum value from a list of integers.

Grabbing the smallest value is obvious:

select min(value) from table;

But the second smallest is not so obvious.

For the record, this list of integers is not sequential — the min can be 1000, and the second most min can be 10000.

Answer 1

Use an analytic function

SELECT value
  FROM (SELECT value,
               dense_rank() over (order by value asc) rnk
          FROM table)
 WHERE rnk = 2

The analytic functions RANK, DENSE_RANK, and ROW_NUMBER are identical except for how they handle ties. RANK uses a sports-style process of breaking ties so if two rows tie for a rank of 1, the next row has a rank of 3. DENSE_RANK gives both of the rows tied for first place a rank of 1 and then assigns the next row a rank of 2. ROW_NUMBER arbitrarily breaks the tie and gives one of the two rows with the lowest value a rank of 1 and the other a rank of 2.