The title does not really tells the whole story, but two versions of a software caused some discombobulation in the data, and I am trying to fix the problem.  Imagine this scenario:

`create table t0 (a, b, idate, PRIMARY KEY (a,idate));
insert into t0 (a, b, idate) values ('p001', '', '2019-02-11');
insert into t0 (a, b, idate) values ('p002', '', '2019-02-11');
insert into t0 (a, b, idate) values ('p003', '', '2019-02-11');
insert into t0 (a, b, idate) values ('p004', '', '2019-02-11');
insert into t0 (a, b, idate) values ('p005', '', '2019-02-11');
insert into t0 (a, b, idate) values ('p001', 'n', '2019-02-12');
insert into t0 (a, b, idate) values ('p002', 'n', '2019-02-12');
insert into t0 (a, b, idate) values ('p003', 'y', '2019-02-12');
insert into t0 (a, b, idate) values ('p004', 'n', '2019-02-12');
insert into t0 (a, b, idate) values ('p005', 'y', '2019-02-12');
insert into t0 (a, b, idate) values ('p001', '', '2019-02-13');
insert into t0 (a, b, idate) values ('p002', '', '2019-02-13');
insert into t0 (a, b, idate) values ('p003', '', '2019-02-13');
insert into t0 (a, b, idate) values ('p004', '', '2019-02-13');
insert into t0 (a, b, idate) values ('p005', '', '2019-02-13');
insert into t0 (a, b, idate) values ('p001', '', '2019-03-14');
insert into t0 (a, b, idate) values ('p002', '', '2019-03-14');
insert into t0 (a, b, idate) values ('p003', '', '2019-03-14');
insert into t0 (a, b, idate) values ('p004', '', '2019-03-14');
insert into t0 (a, b, idate) values ('p005', '', '2019-03-14');
`

What I am trying to do is to update b with the first b value where b is not '' for the rest of the records after that first found b value != ''. So, for all idate > than the idate where the first non '' value was found. So, I thought that this would work:

`
UPDATE t0
    SET b = 
	(
	    select b from t0 where b != '' GROUP BY a
	)
	AND a = 
	(
	    select a from t0 where b != '' GROUP BY a
	)
	AND idate > 
	(
	    select idate from t0 WHERE b != '' GROUP BY a
	)
;
`

But this does not work. It sets all values to 0:

`
sqlite> select a, b, idate from t0 where b != '' group by a;
p001|0|2019-02-11
p002|0|2019-02-11
p003|0|2019-02-11
p004|0|2019-02-11
p005|0|2019-02-11
`

Any thoughts, help would be greatly appreciated.

Do you mean something like this:

```
update t0
   set b = coalesce((select b
                       from t0 as s
                      where a == t0.a
                        and idate < t0.idate
                        and b != ''
                   order by idate desc
                      limit 1), b)
  where b == ''
;
```