mysqldump with INSERT ... ON DUPLICATE I want to merge data from one database to another. So I create dump with mysqldump and then import it to another database (with same tables structure). I don't have any problems (such as duplicate entries or something else) in this case. 

But I do some merges for testing purposes and I'll do final merge later. So, I want to execute merge (data may be changed) a few times. Notice, my rows in my tables never deletes, only can be inserted or updated.

Can I create mysqldump with ON DUPLICATE option? Or may be I can merge dump that inserts new data and update modified data?

Sure, I can insert ON DUPLICATE in dump manually, but I want to automate merge process.
There are options to help you in this:

  --insert-ignore     Insert rows with INSERT IGNORE.
  --replace           Use REPLACE INTO instead of INSERT INTO.
  -t, --no-create-info
                      Don't write table creation info.


Keep this paradigm in mind


mysqldump everything from DB1 into DUMP1
load DUMP1 into DB3
mysqldump everything from DB2 using --replace (or --insert-ignore)
and --no-create-info into DUMP2
load DUMP2 into DB3