ADQL XMATCH

[Tom McGlynn (NASA/GSFC Code 660.1)]

Note that

     distance (point, point)

is already in the standard so what you suggest is already fully supported.

     Tom


Walter Landry wrote:
> "Tom McGlynn (NASA/GSFC Code 660.1)" <tom.mcglynn at nasa.gov> wrote:
>> However if the xmatch function is doing what I indicated above, I
>> think the whole function is superfluous.
>>
>> Rather than
>>      (xmatch(ra1,dec1,ra2,dec2,rad) = 1)
>> or if we use a logical value
>>     (xmatch(ra1,dec1,ra2,dec2,rad))
>>
>> it seems far more natural to use
>>      (distance(ra1,dec1,ra2,dec2) < rad)
> I do like this since it has a certain economy and does not introduce a
> new keyword.  I still like types, so I would write it using the point
> literals as
>
>    distance(db_table.pos,{ra,dec}) < radius
>
> I must note that implementing the more sophisticated example would
> require spatial support directly in the database.  So it would not
> work for our backends.
>
> Cheers,
> Walter Landry