MySQL insert on duplicate update for non-PRIMARY key

Question

I am little confused with insert on duplicate update query. I have MySQL table with structure like this:

• record_id (PRIMARY, UNIQUE)
• person_id (UNIQU

Answer 1

A flexible solution should retain the atomicity offered by INSERT ... ON DUPLICATE KEY UPDATE and work regardless of if it's autocommit=true and not depend on a transaction with an isolation level of REPEATABLE READ or greater.

Any solution performing check-then-act across multiple statements would not satisfy this.

Here are the options:

If there tends to be more inserts than updates:

INSERT INTO table (record_id, ..., some_text, some_other_text) VALUES (...);

IF 
  UPDATE table SET some_text = ..., some_other_text = ... WHERE record_id = ...;

  IF affected-rows = 0
    -- retry from INSERT OR ignore this conflict and defer to the other session

If there tends to be more updates than inserts:

UPDATE table SET some_text = ..., some_other_text = ... WHERE record_id = ...;

IF affected-rows = 0
  INSERT INTO table (record_id, ..., some_text, some_other_text) VALUES (...);

  IF 
    -- retry from UPDATE OR ignore this conflict and defer to the other session

If you don't mind a bit of ugliness, you can actually use INSERT ... ON DUPLICATE KEY UPDATE and do this in a single statement:

INSERT INTO table (record_id, ..., some_text, some_other_text) VALUES (...)
    ON DUPLICATE KEY UPDATE
      some_text = if(record_id = VALUES(record_id), VALUES(some_text), some_text),
      some_other_text = if(record_id = VALUES(record_id), VALUES(some_other_text), some_other_text)

IF affected-rows = 0
  -- handle this as a unique check constraint violation

Note: affected-rows in these examples mean affected rows and not found rows. The two can be confused because a single parameter switches which of these values the client is returned.

Also note, if some_text and some_other_text are not actually modified (and the record is not otherwise changed) when you perform the update, those checks on affected-rows = 0 will misfire.