Sql 在 SCD2 上使用自联接更新查询

Question

I am facing an issue with SQL update query in with self join. I have looked into multiple pages here but didn't find the right solution.

Suppose I have a table like below.

id	country	city	timestamp
1
1	India	Pune	222
1	India	Delhi	111

I want to copy country and city from the max(timestamp) row where they are not null ( group by id ).

I was trying below query which obviously needs correction.

update a1 
set a1.country = a2.country,
    a1.city = a2.city  
from selfjointable a1
inner join selfjointable a2 on (a1.id = a2.id)
where a1.country is null 
  and a2.country is not null 
  and a2.timestamp = (select max(a3.timestamp) 
                      from selfjointable a3 
                      where (a3.id = a1.id)                      
                      group by a3.id);

Please note: This is just simplified version of my issues and there are numbers of rows and column and I just want to write generic update query for all of these rows

Answer 1

How about merge ?

SQL> select * from test order by id, timestamp desc nulls last;

        ID COUNTRY CITY    TIMESTAMP
---------- ------- ------ ----------
         1 India   Pune          222  --> MAX timestamp for ID = 1; these values ...
         1 India   Delhi         111
         1                            --> ... should be copied here
         2 Croatia Zagreb        333

SQL> merge into test a
  2    using (select id, country, city, timestamp,
  3             row_number() over (partition by id order by timestamp desc nulls last) rn
  4           from test
  5          ) x
  6    on (x.id = a.id and x.rn = 1)
  7    when matched then update set
  8      a.country = x.country,
  9      a.city = x.city,
 10      a.timestamp = x.timestamp
 11    where a.country is null;

1 row merged.

SQL> select * from test order by id, timestamp desc nulls last;

        ID COUNTRY CITY    TIMESTAMP
---------- ------- ------ ----------
         1 India   Pune          222
         1 India   Pune          222
         1 India   Delhi         111
         2 Croatia Zagreb        333

SQL>

Answer 2

Below query worked:

UPDATE selfjointable a1
SET (a1.country, a1.city) = (
   SELECT a2.country, a2.city
   FROM selfjointable a1
   WHERE (a1.id=a2.id)
   AND a2.timestamp = (
      SELECT max(a3.timestamp)
      FROM selfjointable a3
      WHERE (a3.id = a2.id) Group by a3.id
   )
)
WHERE a1.country is null