You need a third table where you store the timestamp of the last run or an additional field in Table1 which tells if a record has been processed already. (or does the Date column carry this information?).
then you have to know if all possible combinations of Name and Item are already in Table2. If so a simple update would do the job. If not you should have a look at the merge statement:
It depends on how you know if a row has been "added after last run". If it's all the rows that have NULL in the dt column, then, as suggested above, then you could use MERGE like this:
SELECT GREATEST ( SYSDATE
, MAX (dt) -- DATE is not a good column name
+ INTERVAL '1' SECOND
SET dt = run_date
WHERE dt IS NULL;
SELECT name, item
, COUNT (*) AS cnt
WHERE dt = run_date
GROUP BY name, item
ON ( dst.name = src.name
AND dst.item = src.item
WHEN MATCHED THEN UPDATE
SET dst.cnt -- COUNT is not a good column nae
= NVL (dst.cnt, 0) + src.cnt
WHEN NOT MATCHED THEN INSERT (dst.name, dst.item, dst.cnt)
VALUES (src.name, src.item, src.cnt);
If you'd care to post a little sample date (CREATE TABLE and INSERT statements) for both tables, and the results you want from that data, then I could test this.
Always say what version of Oracle you're using (e.g. 184.108.40.206.0).
See the forum FAQ: https://forums.oracle.com/message/9362002
This assumes that name and item in table_1 are never NULL. If either can be NULL, the same basic approach will still work, but the details are a little more complicated.