SqlJoinedTable represents a joined data source in a SqlStatement.
SqlJoinedTable implements ITableInfo because in SqlPreparationFromExpressionVisitor.VisitMemberExpression, a SqlTable is created that needs to preserve all information about a join (causes by a member access in a from expression). The SqlJoinedTable is used as an adapter between IJoinInfo and ITableInfo. (Refactoring this is definitely possible, e.g., by writing a dedicated adapter class.)