Group by multiple fields and then fetch the most recent record

Table structure: create table test_tmp (
id int,
log_time datetime,
item varchar (10)
)
create table test_d (
id int,
name varchar (10)
)

Test data:
insert into test_d values (1, "hh");
insert into test_d values (2," xx");
insert into test_tmp values (1, "2018-08-16 16 hh" 13 hh" 36 cycles," a");
insert into test_tmp values (1, "2018-08-16 16 13 hh" 36 cycles," b");
insert into test_tmp values (1, "2017-08-16 16 13 hh" 36 cycles," a");
insert into test_tmp values (1, "2017-08-16 16 br 1336," b");
insert into test_tmp values (1, "2018-08-16 16 13 br 36," a");
insert into test_tmp values (2, "2018-08-16 16 br 1336," a");
insert into test_tmp values (2, "2018-08-16 16 br 1336," b");
insert into test_tmp values (2, "2017-08-16 16 br 1336," a");
insert into test_tmp values (2, "2017-08-16 16 13 br 36," b");
insert into test_tmp values (2, "2017-08-16 16 13 13 36," c");

I can only get all of what I write now. How can I get the item (separated by commas) of the most recent record (time) of each id?
select * from test_d d left join (select id, log_time, group_concat (item) from test_tmp group by id, log_time) t on d.id = t.id

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Mysql sql
Dec.08,2021

Let's take it step by step. First of all, the recent time of each test_tmp.id should be taken as follows: 

SELECT id, max(log_time) AS log_time
FROM test_tmp 
GROUP BY id;

secondly, according to the latest time, we can wrap another layer on the outside: 

SELECT
    t1.id, t1.log_time, group_concat(t1.item)
FROM test_tmp t1
INNER JOIN (
    SELECT id, max(log_time) AS log_time
    FROM test_tmp 
    GROUP BY id
) t2 ON t1.id = t2.id AND t1.log_time = t2.log_time
GROUP BY t1.id, t1.log_time;

in this way, we can find out which records correspond to the most recent time based on the most recent time, and on this basis, group_concat can find out the item of the most recent time.
and you can see that the above sql statement is not associated with the test_d table. If you need the id in the test_tmp to be the id, in the test_ d table, you can try it again.

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