Hey, this is cool. I had a query like so:

SELECT stuff
FROM table
WHERE
col = ( SELECT col FROM table_2 WHERE id IN (1,2,3) )

And the sub query was returning NULL sometimes. So I wanted the rows from table where col is null. But the syntax to do that would be:

SELECT stuff
FROM table
WHERE
col IS ( SELECT col FROM table_2 WHERE id IN (1,2,3) )

Now this query isn't going to work when the sub query returns a number. The answer is to use this funky operator thatsolves this problem <=>, the null safe equality operator:

SELECT stuff
FROM table
WHERE
col <=> ( SELECT col FROM table_2 WHERE id IN (1,2,3) )

Smooth :-)