If you're importing or migrating your WordPress database to a server that has an older version of MySQL (like version 5.5.x), you may run into this error:Unknown collation: ‘utf8mb4_unicode_520_ci’
The utf8mb4_unicode_520_ci collation is available in MySQL versions 5.6.x and newer, and WordPress utilizes that collation if it's available during installation. To be able to successfully import or migrate to a server with an older MySQL version, you have one of three options:
If you have the exported .sql file, you can do a simple Find & Replace using a text editor such as Notepad++, replacing all occurrences of utf8mb4_unicode_520_ci with utf8mb4_unicode_ci:
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