I currently have a PHP script that inserts thousands to millions of rows into an InnoDB table. To prevent duplicates, the table has a UNIQUE index set up on the combination of four columns, and I use INSERT IGNORE to allow the insert to continue regardless of duplicates.

For performance reasons, rather than inserting one row at a time, I batch them up into 2000 rows per query. I want to know which individual rows are ignored due to a key violation, and the only way I can think to do it is to insert one row at a time and then check the value of mysqli_affected_rows after each insert, but that feels inefficient and I will lose the advantage of batching my inserts. Alternatively I could remove the UNIQUE index and retrospectively check for duplicates using some SQL at the end.

Any other suggestions?

Many thanks.

1 Answer 1


This can probably be solved with a more complex set of steps. You still get the benefit of the bulk INSERT.

Build a temp table (probably permanent, but TRUNCATE between uses).

INSERT the 2K rows into it.

Analyze the rows via a JOIN between the temp table and the real table.

INSERT INTO real ... SELECT ... JOIN ... to put the "new" rows.

More details in http://mysql.rjweb.org/doc.php/staging_table , especially the section on 'Normalization', which uses two queries in a slightly different way -- one to insert 'new' rows, another to pull back the id for every row.

Your app may also benefit from the "flip-flop" technique described there.

  • I haven't yet had a chance to experiment with this but wanted to thank you in the meantime for your suggestion. Using some kind of temp table certainly makes sense :)
    – Ben Price
    Commented Jan 16, 2018 at 16:03

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.