Count with IF condition in MySQL query

Question

I have two tables, one is for news and the other one is for comments and I want to get the count of the comments whose status has been set as approved.

SELECT
    ccc_news . *, 
    count(if(ccc_news_comments.id = 'approved', ccc_news_comments.id, 0)) AS comments
FROM
    ccc_news
    LEFT JOIN
        ccc_news_comments
    ON ccc_news_comments.news_id = ccc_news.news_id
WHERE
    `ccc_news`.`category` = 'news_layer2'
    AND `ccc_news`.`status` = 'Active'
GROUP BY
    ccc_news.news_id
ORDER BY
    ccc_news.set_order ASC
LIMIT 20 

But the problem with this query is that the minimum value that is fetched for the comments column is 1 whether there is any comment existent corresponding to that news or not.

Any help would be highly appreciable.

Answer 1

Use sum() in place of count()

Try below:

SELECT
    ccc_news . * , 
    SUM(if(ccc_news_comments.id = 'approved', 1, 0)) AS comments
FROM
    ccc_news
    LEFT JOIN
        ccc_news_comments
    ON
        ccc_news_comments.news_id = ccc_news.news_id
WHERE
    `ccc_news`.`category` = 'news_layer2'
    AND `ccc_news`.`status` = 'Active'
GROUP BY
    ccc_news.news_id
ORDER BY
    ccc_news.set_order ASC
LIMIT 20 

Answer 2

Better still (or shorter anyway):

SUM(ccc_news_comments.id = 'approved')

This works since the Boolean type in MySQL is represented as INT 0 and 1, just like in C. (May not be portable across DB systems though.)

As for COALESCE() as mentioned in other answers, many language APIs automatically convert NULL to '' when fetching the value. For example with PHP's mysqli interface it would be safe to run your query without COALESCE().

Answer 3

This should work:

count(if(ccc_news_comments.id = 'approved', ccc_news_comments.id, NULL))

count() only check if the value exists or not. 0 is equivalent to an existent value, so it counts one more, while NULL is like a non-existent value, so is not counted.

Answer 4

Replace this line:

count(if(ccc_news_comments.id = 'approved', ccc_news_comments.id, 0)) AS comments

With this one:

coalesce(sum(ccc_news_comments.id = 'approved'), 0) comments

Answer 5

count(ccc_news_comments.id = 'approved' or null)

More concise