Docs: Add unnest to SQL Reference

[gloomweaver]

Which issue does this PR close?

Closes #.

Rationale for this change

What changes are included in this PR?

Are these changes tested?

Are there any user-facing changes?

[alamb]

Thank you so much @gloomweaver -- this is great. I have another suggestion for documenting unnest for structs as well.

[alamb]

unnest also works for structs. Can you possibly add this example too?

> create table foo as values (named_struct('a', 5, 'b', 'a string'));
0 row(s) fetched.
Elapsed 0.008 seconds.

> select * from foo;
+---------------------+
| column1             |
+---------------------+
| {a: 5, b: a string} |
+---------------------+
1 row(s) fetched.
Elapsed 0.003 seconds.

> select unnest(column1) from foo;
+-----------------------+-----------------------+
| unnest(foo.column1).a | unnest(foo.column1).b |
+-----------------------+-----------------------+
| 5                     | a string              |
+-----------------------+-----------------------+
1 row(s) fetched.
Elapsed 0.003 seconds.

[alamb]

We could merge this PR as is, as well

[gloomweaver]

Yeah, sure. This should be in Struct Functions right?

[comphead]

I would also love to add a range example

select unnest(range(0, 100000))

[alamb]

Yeah, sure. This should be in Struct Functions right?

I think that would make sense.

FWIW here is an example:

DataFusion CLI v39.0.0
> select unnest(range(0, 10));
+-----------------------------------+
| unnest(range(Int64(0),Int64(10))) |
+-----------------------------------+
| 0                                 |
| 1                                 |
| 2                                 |
| 3                                 |
| 4                                 |
| 5                                 |
| 6                                 |
| 7                                 |
| 8                                 |
| 9                                 |
+-----------------------------------+
10 row(s) fetched.
Elapsed 0.054 seconds.

[gloomweaver]

Added docs for struct unnest and example this range for array.
Couldn't link to it because of the name.
Is there a way to assign custom id to a block with sphinx? Tried labels, didn't work, so named it unnest (struct).

[alamb]

Is there a way to assign custom id to a block with sphinx? Tried labels, didn't work, so named it unnest (struct).

I am not sure to be honest

[comphead]

love it, thanks @gloomweaver

[comphead]

@gloomweaver please run the prettier locally, it will reformat the MD files a little bit

[comphead]

  # if you encounter error, rerun the command below and commit the changes
  #
  # ignore subproject CHANGELOG.md because they are machine generated
  npx [email protected] --write \
    '{datafusion,datafusion-cli,datafusion-examples,dev,docs}/**/*.md' \
    '!datafusion/CHANGELOG.md' \
    README.md \
    CONTRIBUTING.md

[alamb]

I took the liberty of running prettier locally to save @gloomweaver the trouble of installing it locally

[alamb]

Thanks so much @gloomweaver and @comphead

[alamb]

❤️

[alamb]

Thanks again @gloomweaver and @comphead