Check out example codes for "mysql count vs sum". It will help you in understanding the concepts better.

Code Example 1

+----+------+
| id | vote |
+----+------+
|  1 |    1 |       COUNT(vote) = 5 
|  2 |   -1 |		SUM(vote) = 1  = (-2 + 3 = 1)
|  3 |    1 |			  
|  4 |   -1 |	#Sum is doing the mathematical sum, whereas count simply 
|  5 |    1 |	#counts any value as 1 regardless of what data type.
+----+------+

/**
The first query returns the number of times the condition is true, because true is 1 and false is 0.
The second query returns the complete record count because count() does not care about the content inside it, as long as the content is NOT NULL. Because count(1) and count(0) are still values and both get counted.
To get the correct return value for the second query you would have to make the result of the condition be null (instead of 0) to not being counted. Like this:
*/
SELECT COUNT(case when USER_NAME = 'JoeBlow' then 'no matter what' else NULL end) 
from your_table

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