How to use COUNT with multiple columns?
There are several things you can count with COUNT() function:


count(*) : rows
count(col1) : rows where col1 is not null
count(col2) : rows where col2 is not null
count(distinct col1) : distinct col1 values.
count(distinct col2) : distinct col2 values.
count(distinct col1, col2) : distinct (col1, col2) values combinations.


Tested at SQLfiddle:

    select 
        count(*)             as count_rows,
        count(col1)          as count_1,
        count(col2)          as count_2,
        count(distinct col1) as count_distinct_1,
        count(distinct col2) as count_distinct_2,
        count(distinct col1, col2) as count_distinct_1_2
    from demo ;


But count(col1, col2) is not valid syntax:

select 
    count(col1, col2) 
from demo ;


gives an error:


  You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'col2) from demo' at line 2.