Grammar fix for DISTANCE

[gmantele]

According to the following rules (v2.1), a DISTANCE function can accept only POINT functions and column references:

<distance_function> ::=
  DISTANCE <left_paren>
              <coord_value> <comma>
              <coord_value>
           <right_paren>
  | DISTANCE <left_paren>
               <numeric_value_expression> <comma>
               <numeric_value_expression> <comma>
               <numeric_value_expression> <comma>
               <numeric_value_expression>
             <right_paren>
 
<coord_value> ::= <point> | <column_reference>

So, it makes impossible to write the following ADQL query:

SELECT TOP 10 CENTROID(s_region),
              DISTANCE(CENTROID(s_region), POINT('', 187.48, 2.05))
FROM ivoa.ObsCore

Since CENTROID returns a POINT, the above query should be correct.

This issue is a request to change the BNF so that a coord_value includes the CENTROID function:

<coord_value> ::= <point> | <column_reference> | <centroid>

coord_value being used only by DISTANCE, COORD1 and COORD2, this modification would be totally harmless. Of course, any other suggestion of modification allowing the usage of CENTROID in DISTANCE is welcome.

--
This issue has been originally raised by @almicol and @vforchi on another GitHub issue in the gmantele/taplib repository.

[almicol]

May I ask if there are news about this issue? Thanks!!!

[almicol]

I'd like to poll the status of this old ticket: any news on this topic? Thanks!

[almicol]

To clarify: my issue is that, while the query (1) below works well,
Query 1:
SELECT count(*) from ivoa.ObsCore where DISTANCE(point('',s_ra,s_dec), s_region) > 0.1
(successful)

the query (2) does not:
Query 2:
SELECT count(*) from ivoa.ObsCore where DISTANCE(point('',s_ra,s_dec), centroid(s_region)) > 0.1
error:
Incorrect ADQL query: Encountered "DISTANCE". Was expecting one of: "(" "NOT" "(" "(" "(" "(" "("
(HINT: "DISTANCE" is a reserved ADQL word. To use it as a column/table/schema name/alias, write it between double quotes.)

The error is due to the fact that DISTANCE does not suppot the CENTROID.