Determines how many times
Self appears in
This trait is primarily used to determine whether or not a column is selectable from a given from clause. A column can be selected if its table appears in the from clause exactly once.
We do not allow the same table to appear in a query multiple times in any context where referencing that table would be ambiguous (depending on the context and backend being used, this may or may not be something that would otherwise result in a runtime error).
How many times does
Self appear in