[ADQL] Reserved keywords

[Gregory MANTELET]

Hi DAL,

Following the discussion about reserved keyword used as 
schema/table/column name.

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=> 1) Am I the only one thinking that some reserved keywords should not 
be reserved in ADQL?

I think at least to `public`. There is a reason why it is reserved in 
SQL (exactly because some DBMS uses it as default schema), but in ADQL, 
I don't see any.
I also think to `distance` and `date` that could often used as column 
name/alias.

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Then, we could also think to other SQL language words such as `CREATE`, 
`DELETE`, `INSERT`, `BEGIN`, `COMMIT`, ... They are used in SQL to 
update the content of the database or to change its structure.

=> 2) Since in ADQL we just have interrogation, is it a good idea to be 
that strict?

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Personally, I don't really have a strong opinion for 2) but I would tend 
to think that they should stay reserved because we might think (in a far 
far future) to have such features in ADQL. So it is a guarantee that we 
could use these keywords if we want to.

But for 1), I think that at least `public`, `distance`, `date`, and 
probably few others should not be reserved.

=> 3a) What do you think?

=> 3b) If there are some keywords that should not be reserved, should we 
start a list somewhere (probably in a GitHub issue?) and start 
discussions to determine whether each of these keywords should really be 
reserved (again, GitHub issue?) ?

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Anyway, if we plan modifications of the ADQL language on this topic, I 
however propose to move that to ADQL-2.2 or -3.0....it is too late for 2.1.

Cheers,
Grégory