in-memory SQL database system [closed]

Question

In an application, I am using mysql's TEMPORARY TABLE. Since this application does not need permanent tables, I wonder if I can find an alternative RDMS designed for memory tables. I hope to find an in-memory database system, which is

1. Lightweight
2. Faster than mysql temporary table
3. Having an API for C (my programming language)

and no special features is needed, just creating table and performing SQL queries. FK or other advanced features are not needed.