MYSQL查询：使用LEFT JOIN

如何解决MYSQL查询：使用LEFT JOIN

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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

我如何修改此查询，使其仅返回num_spam大于0的行。 我尝试把

WHERE `num_spam` > 0

在少数地方，但是没有运气。 谢谢     

解决方法

        您需要一个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

    ,        尝试

GROUP BY jos_mod_gdwcomm.id HAVING num_spam > 0

。     ,        如果要测试聚合函数上的条件，请使用a4ѭ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