Null-safe equal expression (<=> in SQL)

[kevinzwang]

Is your feature request related to a problem?

Right now it is difficult to check the equality of two expressions when we also want nulls to equal each other.

Describe the solution you'd like

Support for the <=> operator in SQL as well as an equivalent Expression in Python DataFrame-land.

It should work as follows:

>>> import daft
>>> df = daft.from_pydict({"a": [1, 2, None], "b": [1, 3, None]})
>>> daft.sql("select a <=> b from df").collect()
╭─────────╮
│ a       │
│ ---     │
│ Boolean │
╞═════════╡
│ true    │
├╌╌╌╌╌╌╌╌╌┤
│ false   │
├╌╌╌╌╌╌╌╌╌┤
│ true    │
╰─────────╯

(Showing first 3 of 3 rows)

Describe alternatives you've considered

No response

Additional Context

No response

Would you like to implement a fix?

No