valenzio valenzio - 1 year ago 70
SQL Question

SQL Query for events that happend in a specific order

I have the following table:

| Object | Event | Time | |
| Obj1 | A | 1 | |
| Obj1 | B | 3 | |
| Obj2 | A | 7 | |
| Obj2 | B | 4 | |

And my goal is to get all objects that both had the event A & B with the condition that A happend first (in time). So far I only came up with the querry to find me all objects that had A & B withouth including the time:

(SELECT * from
(SELECT * FROM table
INNER JOIN (SELECT Object Obj FROM table WHERE event LIKE '%A%' AS temp_table
ON table.Object=temp_table.Obj) AS temp_final WHERE event LIKE '%B%')
AS temp2;

So the end result would be that I get a Table that includes only:


Since this is the only Object that fullfills all criteria.
The time column is a Date stamp in real life, but for simplicity I used integers.
Thanks you for the help

Answer Source

If you are only tracking two events that happened one after the other, than you can solve this with a single JOIN.

This will work regardless of the number of events Obj1 has, as how you mentioned, you are only interested in A and B existing and being one after the other, respectively.

select distinct t1.object
from TABLE t1
    inner join TABLE t2 on t1.object = t2.object
        and t2.time > t1.time
        and t1.event = 'A'
        and t2.event = 'B'

Here is a sample of the result of the code:

declare @tbl table (obj varchar(10), event varchar(1), time int)

insert @tbl values ('Obj1', 'A', 1), ('Obj1', 'B', 3), ('Obj2', 'A', 7), ('Obj2', 'B', 4)

select distinct t1.obj
from @tbl t1
    inner join @tbl t2 on t1.obj = t2.obj
        and t2.time > t1.time
        and t1.event = 'A'
        and t2.event = 'B'
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