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Count with IF condition in MySQL query

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.

What if you use SUM instead of COUNT ?

E
ElChiniNet

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 

Or even SUM(ccc_news_comments.id = 'approved') as a MySQL-specific trick
@mojuba not 100% the same, your trick returns null when COUNT (no conditions) would've returned 0. When COUNT would've returned anything but 0, but the SUM does return 0, your trick returns 0.
@mojuba case and point. num_relevant_parts is SUM with conditions, num_total_parts is COUNT(parts.id) (sorry for double comment, was too late to edit)
p
potashin

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().


This makes for significantly more readable sql code. Beautiful solution.
Always finding this answer when searching for the problem, works as a charm with likely no downsides
A
Alexis Pigeon

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.


I think count is more intuitive than sum in this case.
M
Mosty Mostacho

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

count(if(ccc_news_comments.id = 'approved', ccc_news_comments.id, 0)) ??? what will be meaning of using sum if you use ccc_news_comments.id
Sorry, what do you mean? The boolean value becomes 0 or 1, then sum, and in case there is some null value coalesce with 0
@MostyMostacho, does COALESCE return the sum ? Any reference in MySQL doc ?
Yes, why would't it? There are many references in the docs: dev.mysql.com/doc/refman/5.7/en/…
Z
Zhang Peng
count(ccc_news_comments.id = 'approved' or null)

More concise


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