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.
Warning:
The following query produces a different result for Limbo:
```
select * from demo where value is null or id == 2;
```
I strongly suspect the issue is with the OR implementation, though. The
bytecode generated is quite different.
Reviewed-by: Jussi Saurio <jussi.saurio@gmail.com>
Closes#847
This seems to really be just an alias for IS:
"The IS NOT DISTINCT FROM operator is an alternative spelling for the IS
operator. Likewise, the IS DISTINCT FROM operator means the same thing
as IS NOT. Standard SQL does not support the compact IS and IS NOT
notation. Those compact forms are an SQLite extension. You have to use
the prolix and much less readable IS NOT DISTINCT FROM and IS DISTINCT
FROM operators on other SQL database engines."
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.
Both () and = variants covered. It is important to make sure that
the transaction is a read transaction, so we cannot hide all that logic
inside update_pragma, and have to make our decision before that.
Take the logical OR of the values in register P1 and P2 and store the answer in register P3. If either P1 or P2 is nonzero (true) then the result is 1 (true) even if the other input is NULL. A NULL and false or two NULLs give a NULL output.
Take the logical AND of the values in registers P1 and P2 and write the result into register P3. If either P1 or P2 is 0 (false) then the result is 0 even if the other input is NULL. A NULL and true or two NULLs give a NULL output.
Relates to #127. This PR is still in draft and I have a few left things
to do (tests, improve implementation), just opening it so anyone can
track this work meanwhile.
Closes#664
