Mysql count（）为零时使用case？

我试图得到一个按评论数排序的文章列表。我已经做了类似的过程，以获得一份按Atile的选票排序的列表，但我不知道为什么现在我不能让它工作

SELECT a.*,cc.params as catparams,cc.title as cattitle,u.username,
CASE WHEN CHAR_LENGTH(a.alias) THEN CONCAT_WS(":", a.id, a.alias) ELSE a.id END as slug,
CASE WHEN CHAR_LENGTH(cc.alias) THEN CONCAT_WS(":", cc.id, cc.alias) ELSE cc.id END as   catslug,
CASE WHEN (COUNT(rs.id)=0) THEN 0 ELSE COUNT(rs.id) END as total_comments
FROM jos_content AS a
INNER JOIN table_users AS u ON u.id = a.created_by
INNER JOIN table_categories AS cc ON cc.id = a.catid
LEFT JOIN table__comments AS rs ON rs.id = a.id

此代码仅在文章在comments表中至少有一个条目时返回结果；我想要的是得到所有文章的列表，如果comments表中没有条目，则返回0作为total_comments。我试过内连接、左连接和右连接

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非常感谢您的帮助

我想您需要一个子选择

SELECT 
    a.*,
    cc.params as catparams,
    cc.title as cattitle,
    u.username,
    CASE 
        WHEN CHAR_LENGTH(a.alias) 
        THEN CONCAT_WS(":", a.id, a.alias) 
        ELSE a.id END as slug,
    CASE 
    WHEN CHAR_LENGTH(cc.alias) 
        THEN CONCAT_WS(":", cc.id, cc.alias) 
        ELSE cc.id END as catslug,
    (SELECT COUNT(id) FROM table__comments WHERE id=a.id) as total_comments 
FROM 
    jos_content AS a
    INNER JOIN table_users AS u ON u.id = a.created_by
    INNER JOIN table_categories AS cc ON cc.id = a.catid