[WIP] New SQL command DESCRIBE DATABASE

[gramian]

What does this PR do?

This change adds a new SQL command DESCRIBE DATABASE which returns the value of the also new setting arcadedb.databaseDescription.

Motivation

I wanted a way to convey overall database metadata / comments to a user in a unified way. In standard SQL the command DESCRIBE DATABASE is used to return schema info but semantically "Describe" fits the function rather well.

Additional Notes

• This PR is Work-in-Progress

• Add tests

• @lvca WDYT?

Checklist

• I have run the build using mvn clean package command
• My unit tests cover both failure and success scenarios

[lvca]

Do you mean a describe command like with Oracle?

https://docs.oracle.com/en/database/oracle/oracle-database/19/sqpug/DESCRIBE.html#GUID-2E7032A1-67E9-4E13-96B6-D8F7B138ECAA

Used as describe <type-name|index-name|property-name> ?

[gramian]

Hi

no it works more like this: https://impala.apache.org/docs/build/html/topics/impala_describe.html

But instead of using COMMENT ON DATABASE mydb IS 'bla bla', here I propose to use ALTER DATABASE `arcadedb.databaseDescription` 'bla bla'

And instead of DESCRIBE DATABASE mydb I propose to just use DESCRIBE DATABASE as I can only send SQL queries once I am "in" a database already. Also, this command just returns the comment and not the database name (as you are logged into it) and not the database location (this should be unnecessary info for a user).

[lvca]

What's the purpose of returning a string you set in the settings?

[gramian]

It is supposed to serve as a unified entry point for new users of a database to learn how to get started.

I would put things like this into the description:

This database contains data about X. The central type is the Y vertex (see schema). The types A, B, C are only for purpose P. ...

[gramian]

If you are skeptical with this new command. How about just adding a database setting called databaseDescription?

Since ALTER DATABASE does not support custom attributes there seems to be no other way to store a database global comment.