The main difference between = and != is how null values are handled.
SQLite passes a flag "NULLEQ" to Eq and Ne to disambiguate that.
In the presence of that flag, NULL = NULL.
Some prep work is done to make sure we can pass a flag instead of a
boolean to Eq and Ne. I looked into the bitflags crate but got a bit
scared with the list of dependencies.
The current scheme of combining SQL statements corrupts JSON by dropping
the curly braces. Fix the issue by passing the SQL statement almost as-is
to the database. However, for ".schema" to work, we need to trim extra
whitespace.
