SQL Server tables: what is the difference between @, # and ##?

Question

In SQL Server, what is the difference between a @ table, a # table and a ## table?

Answer 1

I would focus on the differences between #table and @table. ##table is a global temporary table and for the record in over 10 years of using SQL Server I have yet to come across a valid use case. I'm sure that some exist but the nature of the object makes it highly unusable IMHO.

The response to @whiner by @marc_s is absolutely true: it is a prevalent myth that table variables always live in memory. It is actually quite common for a table variable to go to disk and operate just like a temp table.

Anyway I suggest reading up on the set of differences by following the links pointed out by @Astander. Most of the difference involve limitations on what you can't do with @table variables.