Difference between count(*) and count(1) in mysql?
They are the same. This has often been asked in Stackoverflow and here

count(*), count(0), count(1), count(-1)


all return the count.

In fact, in SQL Server, the expression isn't even evaluated. 

Edit In fact, in SQL Server, a COUNT(ALL ...) CONSTANT expression doesn't appear to be evaluated at all, however, a COUNT(DISTINCT ...) is*.

e.g.

select count(ALL 1/0) from xyz; -- Succeeds


but

select count(DISTINCT 1/0) from xyz;  -- Divide by Zero


and at least one exception is NULL

select count(1) from xyz; -- Operand data type void type is invalid for count operator.


FWR in MySQL count(1/0) returns 0 irrespective of the number of rows.