This simplifies the usage and the implementation of the SqliteTableModel
a bit by making the two operating modes it supports (manual query and
interactive query) more obvious in its public interface as well as
simplifying the control flow in the private implementation.
This partially reverts 89587a7d67 to fix
some issues it introduced. Using the knowledge we gained in the further
optimisation process, this commit now gets us the best of both worlds:
good performance when executing complex queries as well as a more
straightforward way to deal with the multithreaded nature of data
loading.
See issue #2537.
This improves the performance of running SQL queries in the
SqliteTableModel class by avoiding an extra query for figuring out the
column names and data types of the returned data.
See issue #2165.
For queries built from a table and filters, use a specialised count query
that only takes into account the where part of the statement. This will
speed-up the Browse Data tab for big tables.
See issue #1666
