Allow usage of table functions in relations

[osipovartem]

Which issue does this PR close?

Closes #16568

Rationale for this change

Allows usage of table functions in relations

SELECT col1, f.* FROM json_tbl, LATERAL FLATTEN(INPUT => col1, PATH => 'name') f;

What changes are included in this PR?

Added section for TableFactor::Function

Are these changes tested?

Tested in fork with registered flatten table function

Are there any user-facing changes?

No

[alamb]

Thank you very much for this contribution @osipovartem -- the code looks great to me but I think we should write test in the datafusion codebase to ensure we don't accidentally break this feature in the future

I think I could write a reproducer using the generate_series function:

> create or replace table json_table (c int) as values (1), (2);

> SELECT c, f.*  FROM json_table, LATERAL generate_series(1,2) f;
This feature is not implemented: Unsupported ast node Function { lateral: true, name: ObjectName([Identifier(Ident { value: "generate_series", quote_style: None, span: Span(Location(1,41)..Location(1,56)) })]), args: [Unnamed(Expr(Value(ValueWithSpan { value: Number("1", false), span: Span(Location(1,57)..Location(1,58)) }))), Unnamed(Expr(Value(ValueWithSpan { value: Number("2", false), span: Span(Location(1,59)..Location(1,60)) })))], alias: Some(TableAlias { name: Ident { value: "f", quote_style: None, span: Span(Location(1,62)..Location(1,63)) }, columns: [] }) } in create_relation

Could you please add a sqllogictest

The instructions how to do so are here: https://github.com/apache/datafusion/blob/main/datafusion/sqllogictest/README.md

I think you could just add a few statements to the end of

datafusion/datafusion/sqllogictest/test_files/table_functions.slt

Line 18 in 85eebcd

# Test generate_series table function

[alamb]

Thank you @osipovartem

[alamb]

I can't merge this PR because it has a conflict that must be resolved. I can't push to the Embucket fork to do it myself. @osipovartem is there any chance you can resolve the conflicts?

[osipovartem]

Let me fix it

[alamb]

Thank you @osipovartem