public interface InsertableRelation
InsertableRelation has the following three assumptions. 1. It assumes that the data (Rows in the DataFrame) provided to the insert method exactly matches the ordinal of fields in the schema of the BaseRelation. 2. It assumes that the schema of this relation will not be changed. Even if the insert method updates the schema (e.g. a relation of JSON or Parquet data may have a schema update after an insert operation), the new schema will not be used. 3. It assumes that fields of the data provided in the insert method are nullable. If a data source needs to check the actual nullability of a field, it needs to do it in the insert method.
void insert(DataFrame data, boolean overwrite)