mysql: find newest non null values - mysql

Question

I have a huge table with 100 fields. Each row is timestamped. I want to find the latest non null value for all columns. I'm using MySql 5.6 InnoDB
e.g.
create table tester(
pub_id int,
pub_name varchar(20),
pub_city varchar(20),
country varchar(20),
no_of_branch varchar(20),
estd datetime
);
insert into tester (pub_id, pub_name, pub_city, country, estd)
values
(1, 'a', 'xyz', 'abcity' , 'a', '1970-01-01 00:00:01'),
(2, 'a', 'xyz', '' , 'a', '1971-01-01 00:00:01'),
(3, 'a', 'xyz', 'abcity1', 'b', '1972-01-01 00:00:01'),
(4, 'a', 'xyz', '' , 'a', '1973-01-01 00:00:01'),
(5, 'a', 'xyz', 'abcity2', '' , '1974-01-01 00:00:01'),
(6, 'b', 'lmn', 'abcity' , 'a', '1974-01-01 00:00:01'),
(7, 'b', 'xyz', '' , 'a', '1975-01-01 00:00:01'),
(8, 'b', 'sdf', 'abcity1', 'b', '1976-01-01 00:00:01'),
(9, 'b', '' , '' , 'a', '1977-01-01 00:00:01'),
(10, 'b', '' , 'abcity2', '' , '1978-01-01 00:00:01');
I want to query that would give me:
'a', 'xyz', 'abcity2', 'a'
'b', 'sdf', 'abcity2', 'b'
I don't want to use a query where i find empty values for each column of the table individually and then take a join as this would be a very cumbersome task given that my actual table has 100 columns.
I have searched for a solution for the past of couple of ours and found nothing. ANy help would be greatly appreciated.
Thanks

Answer 1

This might be the "tricky" way you are looking for.
First create a twin table (tester2) to receive the aggregated data. This new table must have a primary key on pub_name and all the columns you want to aggregate. Then do an INSERT INTO ON DUPLICATE KEY UPDATE. This query will basically rebuild the tester table but without duplicate and with aggregated data. In fact something like this :
insert into tester2 (pub_name, pub_city, country, no_of_branch)
select pub_name, pub_city, country, no_of_branch FROM tester order by estd desc
on duplicate key
update
pub_city = coalesce(tester2.pub_city,tester.pub_city),
country = coalesce(tester2.country,tester.country),
no_of_branch = coalesce(tester2.no_of_branch,tester.no_of_branch)
The content of tester2 will be :
PUB_NAME PUB_CITY COUNTRY NO_OF_BRANCH
a xyz abcity2 a
b sdf abcity2 a
Have a look the DB Fiddle.
Note : I assume you mean real NULL values and not empty string like the sample you provided.