"global temporary tables are visible to all sessions," says the MSDN documentation. I have occasionally wondered when this would be helpful. This week I finally found a use, albeit limited: I want a quick-and-dirty process that will e-mail a CSV file to me every day for a week. I wouldn't do this for a full on production system (without dwelling on it, it just strikes me as too error prone and inelegant), but for some testing I want to do over the course of a week, it makes sense.

I run a query that populates a temp table, and I want to e-mail the contents of the query using sp_send_dbmail. Again, the documentation tells something important: "Note that the query is executed in a separate session, so local variables in the script calling sp_send_dbmail are not available to the query." This applies not just to a table variable, but also a local temp table (e.g. #temp). But a global temp table (e.g. ##temp) is a different story: works just fine. So there you go, quick and dirty way to e-mail yourself some query results when you don't want to just pass the raw query directly to the send command.