clause; columns not explicitly modified retain their previous values.
There are two ways to modify a table using information contained in other tables in the database: using sub-selects, or specifying additional tables in the sub-query that produces as many output columns as are listed in the parenthesized column list preceding it.
The sub-query can refer to old values of the current row of the table being updated.
select * from student; ID NAME SCORE ---------- --------------- ---------- 1 Jack 540 2 Rose 3 William 650 4 Caledon 620 5 Fabrizio 600 6 Thomas 7 Ruth 690 11 Brock 705 10 Lizzy 9 Wallace 600 8 Spicer 620 11 rows selected. But it does not work with a merge query (probably because of the update part): “Missing IN or OUT parameter at index:: 1” Would would you advise to retrieve the value of a field (typically an id) of the row that has been inserted or updated?
Oracle’s MERGE statement is tailor-made for situations when you want to do an "upsert" i.e.
update existing rows in a table or insert new rows depending on a match condition.
A requirement arises in many systems to update multiple SQL database rows.
For small numbers of rows requiring updates, it can be adequate to use an UPDATE statement for each row that requires an update.