How to Avoid Duplicate ID's In Access SQL - sql

Question

I have a problem that I hope you can help me.
I have the next query on Access SQL.
SELECT
ID_PLAN_ACCION, ID_SEGUIMIENTO,
Max(FECHA_SEGUIMIENTO) AS MAX_FECHA
FROM
SEGUIMIENTOS
WHERE
(((ID_PLAN_ACCION) = [CODPA]))
GROUP BY
ID_PLAN_ACCION, ID_SEGUIMIENTO;
And it returns this information:
ID_PLAN_ACCION ID_SEGUIMIENTO MAX_FECHA
-----------------------------------------------
A1-01 1 16/01/2014
A1-01 2 30/01/2014
But I really need that it throws off this:
ID_PLAN_ACCION ID_SEGUIMIENTO MAX_FECHA
----------------------------------------------
A1-01 2 30/01/2014
As you can see I only need the record that has the most recently date, not all the records
The GROUP BY doesn't work.
Please can you tell me what can I do? I am new on all this.
Thank you so much!!
PD: Sorry for my english, I'm learning

Answer 1

This will produce the results you want:
SELECT ID_PLAN_ACCION, max(ID_SEGUIMIENTO) as ID_SEGUIMIENTO, Max(FECHA_SEGUIMIENTO) AS MAX_FECHA
FROM SEGUIMIENTOS
WHERE ID_PLAN_ACCION = [CODPA]
GROUP BY ID_PLAN_ACCION;
I removed id_sequiimiento from the group by and added an aggregation function to get the max value. If the ids increase along with the date, this will work.
Another way to approach this query, though, is to use top and order by:
SELECT top 1 ID_PLAN_ACCION, ID_SEGUIMIENTO, FECHA_SEGUIMIENTO
FROM SEGUIMIENTOS
WHERE ID_PLAN_ACCION = [CODPA]
ORDER BY FECHA_SEGUIMIENTO desc;
This works because you are only returning one row.
EDIT:
If you have more codes, that you are looking at, you need a more complicated query. Here is an approach using where/not exists:
SELECT ID_PLAN_ACCION, ID_SEGUIMIENTO, FECHA_SEGUIMIENTO
FROM SEGUIMIENTOS s
WHERE not exists (select 1
from SEGUIMIENTOS s2
where s.ID_PLAN_ACCION = s2.ID_PLAN_ACCION and
s2.FECHA_SEGUIMIENTO > s.FECHA_SEGUIMIENTO
)
ORDER BY FECHA_SEGUIMIENTO desc;
You can read this as: "Get me all rows from SEGUIMIENTOS where there is no other row with the same ID_PLAN_ACCION that has a larger date". Is is another way of saying that the original row has the maximum date.