How to fix this error
"Running schema recurring.Unique constraint violation found".
This statement occurs when I used upgrade command of Magento 2 model upgradation.
"Running schema recurring.Unique constraint violation found" this occurs if there is duplicate entry in any table of project db and high probability to occur this problem is when you export db and then import,if db is not export completely or correctly.
so the solution is just export db again correctly and import
and if you created tables then define at least one field as unique value in each table