SQL query in PHP ( WordPress )

Question

I need help with a SQL query in PHP ( WordPress ). I have this data:

| id | kw_id | date         | position
| 1  | 1     | 2020.08.23   | 16    |
| 2  | 1     | 2020.10.02   | 17    |
| 3  | 2     | 2020.10.08   | 5     |
| 4  | 2     | 2020.10.08   | 6     |

and I need get two rows ( id=2, id=3 ). Query criteries is two:

1. get row with max date
2. group by kw_id

when date have duplicate ( id=3 and id=4 ) then get row with min position.

The result must be as follows:

id | kw_id | date         | position
2  | 1     | 2020.10.02   | 17
3  | 2     | 2020.10.08   | 5

---

Thanks in advance.

Answer 1

If you are using MySQL 8+, then ROW_NUMBER provides one option:

WITH cte AS (
    SELECT *, ROW_NUMBER() OVER (PARTITION BY id ORDER BY date DESC, position) rn
    FROM yourTable
)

SELECT id, kw_id, date, position
FROM cte
WHERE rn = 1;

The above call to ROW_NUMBER puts the latest date first for each id , and in the case of ties for date, puts the smallest position first.

Answer 2

For legacy MySQL 5.* it can be little complicated. Below query that returns needle id's:

select min(id) as min_id
from tbl
join (
  select kw_id, max(date) max_date
  from tbl
  group by kw_id
) tbl1 on tbl1.max_date = tbl.date and tbl1.kw_id = tbl.kw_id 
group by tbl.kw_id;

result:

+========+
| min_id |
+========+
| 2      |
+--------+
| 3      |
+--------+

and now final query:

select * from tbl where id in (
  select min(id) as min_id
  from tbl
  join (
    select kw_id, max(date) max_date
    from tbl
    group by kw_id
  ) tbl1 on tbl1.max_date = tbl.date and tbl1.kw_id = tbl.kw_id 
  group by tbl.kw_id
);

and final result:

+====+=======+============+==========+
| id | kw_id | date       | position |
+====+=======+============+==========+
| 2  | 1     | 2020-10-02 | 17       |
+----+-------+------------+----------+
| 3  | 2     | 2020-10-08 | 5        |
+----+-------+------------+----------+

and here live SQL fiddle