How to select the last record of each ID

Question

I need to extract the last records of each user from the table. The table schema is like below.

mytable

product | user_id |
-------------------
   A    |   15    |
   B    |   15    |
   A    |   16    |
   C    |   16    |
-------------------

The output I want to get is

product | user_id |
-------------------
   B    |   15    |
   C    |   16    |

Basically the last records of each user.

Thanks in advance!

Answer 1

You can use a window function called ROW_NUMBER .Here is a solution for you given below. I have also made a demo query in db-fiddle for you. Please check link Demo Code in DB-Fiddle

WITH CTE AS
(SELECT product, user_id,
       ROW_NUMBER() OVER(PARTITION BY user_id order by product desc)
       as RN
FROM Mytable)
SELECT product, user_id FROM CTE WHERE RN=1 ;

Answer 2

There is no such thing as a "last" record unless you have a column that specifies the ordering. SQL tables represent unordered sets (well technically, multisets).

If you have such a column, then use distinct on :

select distinct on (user_id) t.*
from t
order by user_id, <ordering col> desc;

Distinct on is a very handy Postgres extension that returns one row per "group". It is the first row based on the ordering specified in the order by clause.

Answer 3

You can try using row_number()

select product,iserid
from
(
select product, userid,row_number() over(partition by userid order by product desc) as rn
from tablename
)A where rn=1

Answer 4

You should have a column that stores the insertion order. Whether through auto increment or a value with date and time.

Ex:

autoIncrement	produt	user_id
1	A	15
2	B	15
3	A	16
4	C	16

SELECT produt, user_id FROM table inner join 
     ( SELECT MAX(autoIncrement) as id FROM table group by user_id ) as table_Aux
     ON table.autoIncrement = table_Aux.id