Question

let’s say I have the following elements:

Actions table

id          type        date
----------- ----------  ----------
1           start       2012-01-01 10:00:00
2           suspend     2012-01-01 11:00:00
3           resume      2012-01-01 12:00:00
4           suspend     2012-01-01 13:00:00
5           resume      2012-01-01 14:00:00
6           stop        2012-01-01 15:00:00
7           refill      2012-01-01 16:00:00
8           stop        2012-01-01 17:00:00

Association table

id    actionID    elementID
----- ----------- -----------
1     1           1
2     2           1
3     3           1
4     4           1
5     5           1
6     6           1
7     7           1
8     8           1

Elements table

id    name
----- -----------
1     my element

So basically I have an element, its status evolves according to some user triggered actions (action table), thoses actions can be shared through many elements (that’s why I have an association table).

What I’d like to retrieve in an SQL query its:

ElementID, start Action ID, last action ID(start action is always linked to an element)

is it possible without writing multiple sql queries ? i’m looking for the most performant query since it’ll run on a table with many millions of entries (the association table & action table)

Thanks

Answer 1

select last.elementID, start.actionID as startAction, last.actionID as lastAction
from (
    select elementID, max(actionID) as actionID
    from Association
    group by elementID
    ) last
inner join (
    select elementID, min(actionID) as actionID
    from Association
    group by elementID
    ) start on start.elementID = last.elementID