3. A First Query

To follow the examples, start TOPCAT and select TAP in the VO menu. Click the pin icon in the upper right corner of the dialog to keep the query window open even while the query is executing..

In TAP URL: at the bottom of the window, enter http://dc.g-vo.org/tap in and click “Use Service’.

At the bottom of the form, at Mode: check “Synchronous"and enter

SELECT TOP 1 1+1 AS result FROM ivoa.obscore

in the text box, then click

"Ok". This should give you a table with a single 2 in it. If that hasn’t worked complain.

Copying and Pasting from http://docs.g-vo.org/adql is legal.

Note that in the top part of the dialog there’s metadata on the tables exposed by the service (in particular, the names of the tables and the descriptions, units, etc., of the columns). Use that when you construct queries later.

There are other TAP clients than TOPCAT – after all, we’re talking about a standard protocol. For example, there’s tapsh that emulates a normal, command-line database shell; most of the queries here assume you’re querying against the server with the IVOA id


To get that, typing server ivo://org.g and then completing with Tab should be sufficient.

You can also use TAPHandle, which runs entirely in your browser.

More TAP clients can be found on the IVOA applications page.


Markus Demleitner

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