What is the difference between count(0), count(1).. and count(*) in mySQL/SQL?

Nothing really, unless you specify a field in a table or an expression within parantheses instead of constant values or *

Let me give you a detailed answer. Count will give you non-null record number of given field. Say you have a table named A

select 1 from A
select 0 from A
select * from A

will all return same number of records, that is the number of rows in table A. Still the output is different. If there are 3 records in table. With X and Y as field names

select 1 from A will give you

1
1
1

select 0 from A will give you
0
0
0

select * from A will give you ( assume two columns X and Y is in the table )
X      Y
--     --
value1 value1
value2 (null)
value3 (null)

So, all three queries return the same number. Unless you use

select count(Y) from A 

since there is only one non-null value you will get 1 as output

COUNT(*) will count the number of rows, while COUNT(expression) will count non-null values in expression and COUNT(column) will count all non-null values in column.

Since both 0 and 1 are non-null values, COUNT(0)=COUNT(1) and they both will be equivalent to the number of rows COUNT(*). It's a different concept, but the result will be the same.

Now - they should all perform identically.

In days gone by, though, COUNT(1) (or whatever constant you chose) was sometimes recommended over COUNT(*) because poor query optimisation code would make the database retrieve all of the field data prior to running the count. COUNT(1) was therefore faster, but it shouldn't matter now.