在 MySQL 查询中使用 IF 条件进行计数

2021-11-20 00:00:00 join if-statement count mysql

我有两张表，一张是新闻，一张是评论，我想获取状态已设置为已批准的评论数.

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

但是这个查询的问题在于，无论是否存在与该新闻对应的任何评论，为评论列获取的最小值都是 1.

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.

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Any help would be highly appreciable.

推荐答案

使用 sum() 代替 count()

试试下面:

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

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