Will COALESCE() & ISNULL() always return the same result when 2 parameters are supplied?

Question

If @s is of type VARCHAR(2) with NULL assigned to it, will COALESCE (@s, 'there') and ISNULL (@s, 'there') return the same result?

Answer 1

No. If we execute the following 3 lines:

DECLARE @s VARCHAR(2) = NULL

SELECT COALESCE (@s, 'there')

SELECT ISNULL (@s, 'there')

We'll find COALESCE (@s, 'there') returns "there" and ISNULL (@s, 'there') returns "th". That's because in the case of ISNULL(), 'there' is first implicitly converted to the data type of @s, VARCHAR(2).