按日期显示每人一个结果

Question

in my local website, people can pass a test, and administrator can see the result. before, all the result were display but it was ugly, so I decided to show only the last test people pass. but I'm stuck because I can show only one result per person, but I can't sort him by date :(

SELECT * FROM resultateval join personne using (id) group by id

this is the query who show one result per people and here is the table.

it's supposed to show

654321 / 08-06-2018 / 12 : 02 / 5 / 8 / 1
 A256589 / 05-06-2018 /13 : 05 / 7 / 10 / 2

Thank you!

Answer 1

Because you stored time and date separately, the query you'll need to do this is relatively ugly. We can form an effective timestamp by using ADDTIME to add the heuereeval time to the dateeval date. Then, this is just a basic aggregation join query:

SELECT t1.*
FROM resultateval t1
INNER JOIN
(
    SELECT id, MAX(ADDTIME(dateeval, heureeval)) AS max_date
    FROM resultateval
    GROUP BY id
) t2
    ON t1.id = t2.id AND
       ADDTIME(t1.dateeval, t1.heureeval) = t2.max_date;

Demo

For future reference, avoid storing the date and time separately, unless there is a very good reason for doing so (and I don't see one here).

Edit: As a I feared, based on comments it appears that you have stored your dates as text. You can use the following function call to generate a date based on the date's text:

STR_TO_DATE(dateeval, '%d-%m-%Y')

Just replace in my original query dateeval with the above call to STR_TO_DATE and it should still work.

Answer 2

What you are doing is very wrong. You group by id , but you select all columns. As id is not unique in your joined data, this makes no sense and is invalid SQL. You cannot say: "Give me the dateeval (etc.) for the id ". You must say something like: " "Give me the minimum / maximum / average dateeval for the id ".

This query should result in an error, but MySQL outside ONLY_FULL_GROUP_BY mode let's this slip and silently converts select * to select id, any_value(dateeval), any_value(heureeval) ... . So you get arbitrarily picked values that can even stem from different records.

What you want is something like this:

select *
from resultateval 
join personne using (id)
where (id, timestamp(dateeval,heureeval)) in
(
  select id, max(timestamp(dateeval,heureeval)) 
  from resultateval 
  join personne using (id)
  group by id
);