Fetching last 2 rows of multiple user in MySQL [duplicate] - mysql

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Grouping by a Top N in MySQL
(2 answers)
Closed 2 years ago.
I have a table to list the transaction made by users.
mysql> select * from transaction;
+-----------+----------+------------+
| emp_id_fk | trans_id | trans_date |
+-----------+----------+------------+
| 1 | 1 | 2008-01-01 |
| 1 | 2 | 2019-01-01 |
| 1 | 3 | 2020-01-01 |
| 2 | 4 | 2020-01-10 |
| 2 | 5 | 2020-01-16 |
| 2 | 6 | 2020-01-15 |
+-----------+----------+------------+
6 rows in set (0.00 sec)
I want to know the last 2 transactions made by the users along with their transaction ID.
The output should look something like this.
+-----------+----------+------------+
| emp_id_fk | trans_id | trans_date |
+-----------+----------+------------+
| 1 | 2 | 2019-01-01 |
| 1 | 3 | 2020-01-01 |
| 2 | 5 | 2020-01-16 |
| 2 | 6 | 2020-01-15 |
+-----------+----------+------------+
I've tried inner joins and group by clause but of no use. How can I generate this output?

Answer 1

If you are running MySQL 8.0, you can use window fuctions:
select *
from (
select t.*, row_number() over(partition by emp_id_fk order by trans_date desc) rn
from transactions t
) t
where rn <= 2
order by emp_id_fk, trans_date
If there may be more than one transaction for a given customer on the same date, consider adding another sorting criteria to the order by clause of the window function, such as trans_id for example:
row_number() over(partition by emp_id_fk order by trans_date desc, , trans_id) rn desc
In older versions, you could use a correlated subquery:
select t.*
from transactionts t
where (
select count(*)
from transactions t1
where t1.trans_date >= t.trans_date and t1.emp_id_fk = t.emp_id_fk
) <= 2