You can solve this by finding

ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_520_ci;

in your .sql file, and swapping it with

ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_general_ci;

In my case it turns out my
new server was running MySQL 5.5,
old server was running MySQL 5.6.
So I got this error when trying to import the .sql file I’d exported from my old server.

MySQL 5.5 does not support utf8mb4_unicode_520_ci, but
MySQL 5.6 does.

Updating to MySQL 5.6 on the new server solved collation the error !

If you want to retain MySQL 5.5, you can:
– make a copy of your exported .sql file
– replace instances of utf8mb4unicode520_ci and utf8mb4_unicode_520_ci
…with utf8mb4_unicode_ci
– import your updated .sql file.

Open the sql file in your text editor;

1. Search: utf8mb4_unicode_ci Replace: utf8_general_ci (Replace All)

2. Search: utf8mb4_unicode_520_ci Replace: utf8_general_ci (Replace All)

3. Search: utf8mb4 Replace: utf8 (Replace All)

Save and upload!

easy replace

sed -i 's/utf8mb4_unicode_520_ci/utf8mb4_unicode_ci/g' your_sql_file.sql

Getting collation error #1273 – Unknown collation: ‘utf8mb4_unicode_520_ci’ is caused by the difference of the MySQL version from which you export and our MySQL server to which you import. Basically, the WordPress library for newer version checks to see what version of SQL your site is running on. If it uses MySQL version 5.6 or more, it assumes the use of a new and improved Unicode Collation Algorithm (UCA) called “utf8mb4_unicode_520_ci”. This is great unless you end up moving your WordPress site from a newer 5.6 version of MySQL to an older, pre 5.6 version of MySQL.

To resolve this you will either have to edit your SQL export file and do a search and replace, changing all instances of ‘utf8mb4_unicode_520_ci’ to ‘utf8mb4_unicode_ci’. Or follow the steps below if you have a PHPMyAdmin:

1. Click the Export tab for the database
2. Click the Custom radio button.
3. Go the section titled Format-specific options and change the drop-down for Database system or older MySQL server to maximize output compatibility with: from NONE to MYSQL40.
4. Scroll to the bottom and click GO.

In my case I substitute it with utf8_general_ci with sed like this:

sed -i 's/utf8mb4_unicode_520_ci/utf8_general_ci/g' MY_DB.sql 
sed -i 's/utf8mb4_unicode_520_ci/utf8_general_ci/g' MY_DB.sql 

After that, I can import it without any issue.

I simply removed the COLLATE and other attributes and left only till ENGINE.
like the following

FROM:

ENGINE=InnoDB AUTO_INCREMENT=429 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_520_ci

TO:

ENGINE=InnoDB;

and it worked for me just fine.