Difference between utf8mb4_unicode_ci and utf8mb4_unicode_520_ci collations in MariaDB/MySQL?

Question

I logged into MariaDB/MySQL and entered:

SHOW COLLATION;

I see utf8mb4_unicode_ci and utf8mb4_unicode_520_ci amon

Answer 1

I will develop @StuiterSlurf answer and focus on details of utf8mb4_unicode_ci/utf8mb4_unicode_520_ci:

As you can read here (Peter Gulutzan) there is problem with sorting/comparing polish letter "Ł" (L with stroke) (lower case: "ł"; html esc: ł and Ł ) - we have following assumption in coding (same with mb4):

utf8_polish_ci      Ł greater than L and less than M
utf8_unicode_ci     Ł greater than L and less than M
utf8_unicode_520_ci Ł equal to L
utf8_general_ci     Ł greater than Z

In polish language letter Ł is after letter L and before M. And for different coding system you will get different sorting results. No one of this coding is better or worse - it depends of your needs.