Hi,
How are you trying to migrate from MySQL to Oracle? Did you roll your own migrator?
Since 5.6.6 is extremely old I suggest instead that you upgrade through 6.7.7 to 7.8, then use the FLOSS migrator we’ve provided to get off of MySQL, and then upgrade to 7.9.2 - the current LTS - and optionally on up to 8.1.
Ann