Oracle if updating then
One insert takes effect, the second merge neither inserts or updates. KUTUK WHEN NOT MATCHED THEN INSERT ( CILT, SAYFA, KUTUK, MERNIS_NO) VALUES (E. But the insert is an independent command and it has to do a second lookup.
However, the faster approach of doing two separate statements is safe. I don't know the inner workings of the merge command but since the command is a single unit, Oracle could have execute the correct insert or update with a single index lookup.
The check for existence of a match and the insertion of a new record are not protected by a lock, so there is a race condition.
A suggestion: rather than check for existence insert/update, it’s usually more efficient to do it one of these ways: 1.
If you know your source data will have more new records: INSERT; if it fails with DUP_VAL_ON_INDEX then update. If you know your source data will have more changed records: UPDATE; if sql%rowcount is 0 then insert. Thanks for writing this article, I have had to write a data import process and have been using the MERGE statement to really improve performance but found the sequence gaps issue…
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?
create or replace procedure ups(xa number) as begin merge into mergetest m using dual on (a = xa) when not matched then insert (a,b) values (xa,1) when matched then update set b = b 1; end ups; / drop table mergetest; create table mergetest(a number, b number); call ups(10); call ups(10); call ups(20); select * from mergetest; A B ---------------------- ---------------------- 10 2 20 1 Apparently the "merge into" statement is not atomic.
It can result in "ORA-0001: unique constraint" when used concurrently.This is typically the case when you have to synchronize a table periodically with data from another source (table/view/query).In place of 3 separate unwieldy INSERT, UPDATE and DELETE statements with conditional sub-queries, the all-in-one MERGE does the job in one shot.In Oracle 10, you can use the "log errors" clause to make it continue with the rest of the rows when an error occurs and log the offending row to another table, rather than just stopping.Hi, I tried to use same query pattern in my query but somehow my query is inserting duplicate rows.have been thinking of ways around it and have found converting the primary key id of the target table to use an auto-increment trigger prevents the gap happening… z(i) from dual) T2 ON (T1.x = T2.x) WHEN NOT MATCHED insert WHEN MATCHED update This runs very poorly compared to SAVE Exceptions insert and then processing the errors (dup-key) for update Is there a limit to how high the Bulk_Limit can be for such an operation Regards You mentioned in the “Watch out for these when you MERGE’ No.4 about the delete clause, which is not entirely true.