sql - Filling null values with last not null one => huge number of columns -

i want copy rows source_table target_table while filling null values last not null one.

what have :

source_table :        |    b |    c | parent | seq_number        1 |    2 | null |      1 |          1     null | null |    1 |      1 |          2     null |    3 |    2 |      1 |          3  dest_table empty 

what want :

dest_table :        |    b |    c | parent | seq_number        1 |    2 | null |      1 |          1        1 |    2 |    1 |      1 |          2        1 |    3 |    2 |      1 |          3 

to achieve i'm dynamically generating following sql :

insert target_table (a, b, c)   select  coalesce(a, lag(a ignore nulls) on (partition parent order seq_number)) a,           coalesce(b, lag(b ignore nulls) on (partition parent order seq_number)) b,           coalesce(c, lag(c ignore nulls) on (partition parent order seq_number)) c,   source_table;  

everything works fine if source , target tables have small number of columns. in case have 400+ columns (yes bad legacy , cannot changed) , got following error :

ora-01467: sort key long

• first don't understand error. because i'm using many lag functions use "order by"/"partition by" ? replace coalesce(a, lag(a....)) coalesce(a,a) , error disappear.
• then, there workaround or way achieve same result ?

thx

just using pl/sql anonymous block:

declare    x tgt_table%rowtype; --keep values last row begin    r in (select * src_table order seq_number) loop        x.a := nvl(r.a, x.a);        ...        x.z := nvl(r.z, x.z);        insert tgt_table        values x;    end loop; end;