Copy records from one table to another with pl-sql - oracle

Question

I want to copy records from one table to another.
The only records from table 1 that will be copied to table 2 are the ones that still dont exist in table 2.
If duplicate records exists in Table 1 then only be copied to table 2 the record with the larger size name.
I could already implement a query that almost does what I want.
The problem I have is when there are names with the same maximum size of characters.
In these cases, my query returns more than one record and I just want to insert one new record in table 2.
Does anyone know how I can fix this?
Here is my code:
For x in (Select distinct xdd.id_t, xdd.name_t
From table1 xdd
Where xdd.id_t not in (Select distinct det.id_t2
From table2 det)
And LENGTH(xdd.name_t) in (Select Max(LENGTH(xdd2.name_t))
From table1 xdd2
Where xdd2.id_t = xdd.id_t)
) Loop
Insert into id_t2 (id_t2, name_t2)
Values (x.id_t, x.name_t);
End loop;

Answer 1

Can you give me an example to solve this?
Sure. If I understood requirements correctly, then the merge statement will look similar to this one:
We use row_number() analytic function to choose a duplicate record with longer name_t
merge into table_two t2
using(
select id_t
, name_t
from (select id_t
, name_t
, row_number() over(partition by id_t
order by length(name_t) desc) as rn
from table_one) q
where q.rn = 1
) t1
on (t2.id_t = t1.id_t)
when not matched then
insert(id_t, name_t)
values(t1.id_t, t1.name_t)
SQLFiddle demo

Answer 2

This is a merge statement that should "upsert" data from table 1 into table 2. Matching keys should update only when the name field in table1 is greater than that of table 2. And inserts should occur when keys from table one are not matched to table 2.
MERGE INTO table2 D
USING (SELECT table1.id_t, table1.name_t FROM table1) S
ON (D.id_t2 = S.id_t)
WHEN MATCHED THEN UPDATE SET D.name_t2 = S.name_t
WHERE (LENGTH(S.name_t) > LENGTH(D.name_t2))
WHEN NOT MATCHED THEN INSERT (D.id_t, D.name_t)
VALUES (S.id_t2, S.name_t2);