This might help.
As you can see the ^posts table contains a selchildid field. It is nullable foreign key that references the very same table. So, for a given question, when that field is null then the question has no selected answer. When it is assigned a value different than null then the question has a best answer selected. The value, in this case, would be the id of the answer that was selected as best.
Welcome to the Q&A site for Question2Answer.
If you have a question about Q2A, please ask here, in English.
To report a bug, please create a new issue on Github or ask a question here with the bug tag.
If you just want to try Q2A, please use the demo site.
April 20, 2021: Q2A 1.8.6 released!