Count total number of callers?

I'm currently doing this query to find the guy who makes the most calls:

SELECT 
    `commenter_name`, 
    COUNT(*) AS `calls` 
FROM `comments` 
GROUP BY `commenter_name` 
ORDER BY `calls` LIMIT 1

What I want now is to be able to find out how many total unique callers. I tried using DISTINCT开发者_JS百科 but I didn't get anywhere.

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SELECT COUNT(DISTINCT 'commenter_name') FROM 'comment';

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SELECT DISTINCT `commenter_name` FROM `comments`

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Select Count(*) From (Select DISTINCT commenter_name from comment) as CmtCnt;