Monday, December 11, 2017

MySQL - Duplicate Errors & Trailing Whitespace

I had a unique constraint on a VARCHAR column and I inserted two rows with the following values:

  1. "name" (without trailing whitespace)
  2. "name " (with trailing whitespace)

To my surprise, I got a duplicate error on that 2nd insert. It turns out that MySQL ignores that trailing whitespace when it makes comparisons.

The MySQL docs say this: "All MySQL collations are of type PAD SPACE. This means that all CHAR, VARCHAR, and TEXT values are compared without regard to any trailing spaces. “Comparison” in this context does not include the LIKE pattern-matching operator, for which trailing spaces are significant." (

The solution? You should probably be trimming trailing whitespace in your API endpoints and on your front-end.