What is the difference between Collation UNICODE_CI_AI, UNICODE_CI and UNICODE

Collation ) is nothing more than the character encoding in the database. There are settings for character sets and Collations collations on four levels:

When you migrate content from a database, there may be conflicts in the collation of the migrated database. The result of this conflict is the absence of special characters when information is queried in the database.

You have registered the word " José " in your database, but when the programming of your site or system searches for this item, it returns the result " . That is, accented characters such as (é, ã, õ, etc.) are replaced by the "?" (Question mark) or other characters. Source: a a .html # rmcl "> link

• UTF-8
         It is a variable-width character encoding capable of encoding all 1,112,064 valid code points in Unicode using one to four 8-bit bytes . The encoding is defined by the Unicode pattern and was originally designed by Ken Thompson and Rob Pike. The name is derived from the Transformation Format Unicode or ( Universal Coded Character Set ) - 8 bits.

• Collation *
   Each character set has a standard collation sequence (COLLATE) that specifies the collation order. Generally, it provides nothing more than sorting based on the numeric code of the characters and a basic mapping of uppercase and lowercase characters. If any behavior is required for sequences that are not provided by the default merge sequence and an appropriate alternative collation is supported for that character set, a COLLATE collation clause may be specified in the column definition. > A COLLATE collation clause can be applied in contexts other than the column definition. For comparison operations greater than / less than, it can be added in the WHERE clause of a SELECT statement. If the output needs to be sorted in a special alphabetical string, or without distinction between uppercase and lowercase , and the appropriate collation exists, a COLLATE clause may be included with the clause ORDER BY when rows are being sorted in a character field and with the GROUP BY clause in case of collation operations.
  

Collation for UTF8 Character Set: