I had an error after upgrading and fixed is as suggested in right here.
In this thread, the issue seems fixed, but for me, not just yet. Now I've got a similar, but not the same, error:
Error Number: 1060
Duplicate column name 'parent_element_id'
ALTER TABLE exp_playa_relationships ADD parent_element_id VARCHAR(255) NULL AFTER parent_var_id
Filename: third_party/playa/ft.playa.php
Line Number: 488
As they mentioned in the thread, there's a certain amount of things to be checked. If this then, that.
In my case, I had to check if there's a parent_element_id in exp_playa_relationships and, if so, change version to 4.5.2 in exp_fieldtypes.
These checks do feel somewhat more complex though, as you can just change the version to whatever version you're trying to install (which you can see in the Add-Ons -> Fieldtype tab)
