Oracle multiple processes updating same table
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.
Any data that violates any unique index will cause the same problem. For example, I might export some data to a spreadsheet, send it to a client, and the client might update or add some data and return the spreadsheet to me.
That’s a terrible way to update data, but for various reasons, I’m sure many readers have found themselves in a similar situation.
Then the key chosen will be one more than the largest key that has ever existed in that table. You can put arbitrary length strings into integer columns, floating point numbers in boolean columns, or dates in character columns.
Let’s say this is how STUDENT_N looks before it is merged with STUDENT: merge into student a 2 using 3 (select id, name, score 4 from student_n) b 5 on (= b.id) 6 when matched then 7 update set = 8 , a.score = b.score 9 when not matched then 10 insert (a.id, a.name, a.score) 11 values (b.id, b.name, b.score); 5 rows merged.
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?
Note that the integer key is one greater than the largest key that was in the table just prior to the insert.
The new key will be unique over all keys currently in the table, but it might overlap with keys that have been previously deleted from the table.
Consequently, to prevent this, you might do this: One potential issue may arise when the subquery actually finds more than one matching row in tbl B.