MYSQL查询：使用LEFT JOIN

Question

SELECT jos_mod_gdwcomm.*, COUNT(jos_mod_gdwcomm_spam.reportid) `num_spam` 
FROM `jos_mod_gdwcomm` 
WHERE `num_spam` > 0 
LEFT JOIN `jos_mod_gdwcomm_spam` 
ON (jos_mod_gdwcomm.id = jos_mod_gdwcomm_spam.commid) 
GROUP BY jos_mod_gdwcomm.id
ORDER BY `num_spam` DESC, jos_mod_gdwcomm_spam.datetime DESC

如何修改此查询，使其仅返回num_spam大于0的行。

我试着把

WHERE `num_spam` > 0

在一些地方，但没有运气。

由于

Answer 1

你需要一个HAVING子句：

SELECT jos_mod_gdwcomm.*, COUNT(jos_mod_gdwcomm_spam.reportid) `num_spam` 
FROM `jos_mod_gdwcomm` 
LEFT JOIN `jos_mod_gdwcomm_spam` 
ON (jos_mod_gdwcomm.id = jos_mod_gdwcomm_spam.commid) 
GROUP BY jos_mod_gdwcomm.id

HAVING num_spam > 0

ORDER BY `num_spam` DESC, jos_mod_gdwcomm_spam.datetime DESC

Answer 2

尝试使用GROUP BY jos_mod_gdwcomm.id HAVING num_spam > 0。

Answer 3

如果要在聚合函数上测试条件，请使用HAVING子句。

SELECT jos_mod_gdwcomm.*, COUNT(jos_mod_gdwcomm_spam.reportid) `num_spam` 
    FROM `jos_mod_gdwcomm` \
        LEFT JOIN `jos_mod_gdwcomm_spam` 
            ON (jos_mod_gdwcomm.id = jos_mod_gdwcomm_spam.commid) 
    GROUP BY jos_mod_gdwcomm.id
    HAVING COUNT(jos_mod_gdwcomm_spam.reportid) > 0 
    ORDER BY `num_spam` DESC, jos_mod_gdwcomm_spam.datetime DESC