Question

This is kind of hard to explain so I’ll break it down…Here’s the objective

Suppose you have a table

ID | Weight

1     2
2     4
3     8
4     66
5     11 
6     44
7     33

And suppose I have a set of interested IDs, say (3,4)

My objective is to get two other rows (one for each of the two interested IDs) such that the row that matches with the interested ID has a weight that is one level less than the weight of the interested ID

so in this case

for id 3, we want to return row with ID 2 and weight 4 since row id 2 is the first row of which the weight (4) is less than the weight of row id 3 (8)

for id 4, we want to return row with id 6 and weight 44 since row id 6 is the first row of which the weight (44) is less than the weight of row id 4 (66)

How would you accomplish this with mysql in one single query whereby we use the IN() notation for the interested IDs…..

Answer 1

I’d like to propose the following (used ourtable as table name obviously)

SELECT id,weight FROM ourtable WHERE weight IN (SELECT MAX(t.weight) FROM ourtable t,ourtable t2 WHERE t.weight < t2.weight && t2.id IN (3,4) GROUP BY t2.id);

it gives the following result

+----+--------+
| id | weight |
+----+--------+
|  2 |      4 |
|  6 |     44 |
+----+--------+

as requested.