When converting or registering a DataStream or DataSet as Table, the schema of the table can be defined (by default it is extracted from the TypeInformation.
The schema needs to be manually specified to select (project) fields, rename fields, or define time attributes. Right now, there are several limitations how the fields can be defined that also depend on the type of the DataStream / DataSet. Types with explicit field ordering (e.g., tuples, case classes, Row) require schema definition based on the position of fields. Pojo types which have no fixed order of fields, require to refer to fields by name. Moreover, there are several restrictions on how time attributes can be defined, e.g., event time attribute must replace an existing field or be appended and proctime attributes must be appended.
I think we can make the schema definition more flexible and provide two modes:
1. Reference input fields by name: All fields in the schema definition are referenced by name (and possibly renamed using an alias (as). In this mode, fields can be reordered and projected out. Moreover, we can define proctime and eventtime attributes at arbitrary positions using arbitrary names (except those that existing the result schema). This mode can be used for any input type, including POJOs. This mode is used if all field references exist in the input type.
2. Reference input fields by position: Field references might not refer to existing fields in the input type. In this mode, fields are simply renamed. Event-time attributes can replace the field on their position in the input data (if it is of correct type) or be appended at the end. Proctime attributes must be appended at the end. This mode can only be used if the input type has a defined field order (tuple, case class, Row).
We need to add more tests the check for all combinations of input types and schema definition modes.