如何将共享一个相同值的多行折叠成一行 PRESTO SQL

Question

I have this table

id	cnt1	cnt2
7775	1
7775		2

I would like to combine the rows so that it comes out to this

id	cnt1	cnt2
7775	1	2

I've tried a self join but it only appends the rows to the bottom. Any ideas? thank you!

Answer 1

use SubQuery and join as follows

SELECT T1.Id,
       Cnt1,
       Cnt2
FROM   (SELECT Id,
               Cnt1
        FROM   Table
        WHERE  Cnt1 IS NOT NULL) T1
       JOIN (SELECT Id,
                    Cnt2
             FROM   Table
             WHERE  Cnt2 IS NOT NULL) T2
         ON T1.Id = T2.Id  

Answer 2

Depending on required logic you can use group by id with corresponding aggregate function, for example max (or sum ), which will ignore null values.

-- sample data
WITH dataset (id, cnt1, cnt2) AS (
    VALUES (7775, 1, null),
        (7775, null, 2)
) 

-- query
select id,
    max(cnt1) cnt1,
    max(cnt2) cnt2
from dataset
group by id

Output:

id	cnt1	cnt2
7775	1	2