Environment:

Oracle B2C Service Versions 18A and newer, MySQL

Resolution:

MySQL has reserved keywords that should be avoided in custom field, custom object class, or attribute naming. The user interface blocks known reserved keywords in most cases. However, as customers migrate between MySQL 5.1 and MySQL 5.7 the reserved words change and customers that were not affected could become affected by a new reserved word.

Please find the list of reserved words here: https://dev.mysql.com/doc/mysqld-version-reference/en/keywords-5-7.html and rename your custom field, custom object class, and/or attribute names that match a reserved keyword. 

For further details regarding the MySQL update, see Answer ID 9429: Oracle B2C Service 18A: MySQL 5.7 Upgrade - General Announcement