name:: Make a color map from CALIFA cubes
query::
SELECT TOP 20000 raj2000, dej2000, flux3807-flux3839 as color
FROM (
  SELECT obsid, flux as flux3807
  FROM califadr1.fluxv500
  WHERE lambda=3807) AS t1
NATURAL JOIN (
SELECT obsid, flux as flux3839
  FROM califadr1.fluxv500
  WHERE lambda=3839) AS t2
JOIN califadr1.spectra USING (obsid)
WHERE obsid like 'V500/IC0540%'
description:: 
This query shows how to use the :taptable:`califadr1.fluxv500` 
(or :taptable:`califadr1.fluxv1200`) tables to obtain maps of color indices.

The first step is to create two tables that have single-lambda maps of fluxes
for a wavelength each.  Note how we use column aliasing here to allow natural
joining the tables and to have a nice expression in the select clause.

The obsid identifies one spatial pixel here.  This pixel is mapped to a
position in the :taptable:`califadr1.spectra` table, which is subsequently
joined to get the actual sky positions.

Note  that it's fairly easy to turn this into "broadband" colors; you'll 
just have to adjust the inner selects, e.g., like this::

	SELECT obsid, SUM(flux)/count(*) AS flux3839
  	FROM califadr1.fluxv500
  	WHERE lambda BETWEEN 3850 AND 3900
  	GROUP BY obsid) AS t2

Note that queries like this can run for quite a while.  Further note that NULL
values in flux tend to make such images "spotty".  To make things more robust,
you could filter by ``WHERE flux IS NOT NULL`` in yet another inner select.
..