The difference between "select count (null)" and "select count (1)"

Question

In MySQL

Select 1 from mytable

and

select null from mytable

both return the same number of rows. While it select count(1) from mytablereturns a string, it select count(null) from mytablealways returns 0. Why?

Answer 1

COUNT returns the number of non-null values, so it returns 0 for null.