ADQL XMATCH

[Walter Landry]

"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