Added SQL string function documentation and examples

[sanderson]

• Rebased/mergeable

[sanderson]

@alamb I noticed some behavior with some of the string functions that may be a bug. If I need to modify a tag value, I have to explicitly cast the tag column to a string. I know that tags and fields use different arrow types (tags seem to be a key-value pair dictionary), but in the context of InfuxDB, tags are always strings, so casting shouldn't be necessary. For example:

SELECT DISTINCT
  upper(room::STRING)
FROM home

I feel like I should just be able to do the following:

SELECT DISTINCT
  upper(room)
FROM home

Is this something worth filing an issue about? I think this is fairly unique to our implementation of SQL, so if I do create an issue, where should I create it?

[alamb]

Hi @sanderson -- I can reproduce the error you are describing here:

26f7e5a4b7be365b_917b97a92e883afc> select distinct host from cpu;
+---------------------+
| host                |
+---------------------+
| MacBook-Pro-8.local |
+---------------------+

But this fails:

26f7e5a4b7be365b_917b97a92e883afc> select distinct upper(host) from cpu;
Error running remote query: Tonic(Status { code: Internal, message: "Error while planning query: Internal error: The \"upper\" function can only accept strings.. This was likely caused by a bug in DataFusion's code and we would welcome that you file an bug report in our issue tracker", metadata: MetadataMap { headers: {"content-type": "application/grpc", "date": "Thu, 02 Mar 2023 21:27:29 GMT", "content-length": "0"} }, source: None })
26f7e5a4b7be365b_917b97a92e883afc>

I think this is a bug/limitation in DataFusion that should be fixed upstream. I will file a bug.

[alamb]

This looks like great content. Would you be amenable to figuring out how we could move the content into the DataFusion repo (and maybe have a script to sync it over here or something)? That way we could get more reviewers in the community to help review

[sanderson]

My plan is to port all of this content over to the DataFusion docs once it's complete. That will likely be sometime next week. Pulling content from upstream will be a bit of a challenge since not all functionality upstream is applicable downstream in InfluxDB, but we may be able to figure something out.

[alamb]

Filed https://github.com/influxdata/idpe/issues/17251 to track helping this effort

[alamb]

I think this is a bug/limitation in DataFusion that should be fixed upstream. I will file a bug.

apache/datafusion#5471