Question

I have the following table:

create table weights (
   ident int references users,
   dateW date,
   weight float,
   primary key(ident,dateW)
);

I wanna select only the weight from a given user (ident) with the most recent date. I have:

SELECT WEIGHT
FROM WEIGHTS
WHERE WEIGHTS.IDENT = 22 AND WEIGHTS.DATEW = (SELECT MAX(WEIGHTS.DATEW)
                                              FROM WEIGHTS);

But it’s not doing what I want. Suggestions?

Answer 1

You can use a subquery:

SELECT w.WEIGHT
FROM WEIGHTS w
INNER JOIN
(
    SELECT MAX(DATEW) MaxDATEW
    FROM WEIGHTS 
) w1
    on w.DATEW= w1.MaxDATEW
WHERE w.IDENT = 22 

Or you can apply row_number()

select *
from
(
    SELECT w.WEIGHT, row_number() over(order by w.DATEWdesc) rn
    FROM WEIGHTS w
    WHERE w.IDENT = 22 
) s
where rn = 1