mybatis Result Maps對結果分組3--一對多使用limit

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前面兩篇文章都是先把多張表的結果一並取出，然后用mybatis自動分組，實現一對多的結果集。但是，實際開發過程中，是需要對評論分頁的，比如在mysql中使用limit.

SELECT articlecomment.articlecomment_id,articlecomment.commenttime,articlecomment.commentcontent,articlecomment.id as commentuser_id
,articlereply.articlereply_id,articlereply.replytime,articlereply.replycontent,articlereply.id as replyuser_id
,u1.name AS comment_user,u2.name AS reply_user FROM articlecomment 
LEFT JOIN articlereply ON articlereply.comment_id=articlecomment.articlecomment_id INNER JOIN USER AS u1 ON u1.id=articlecomment.id 
INNER JOIN USER AS u2 ON u2.id=articlereply.id ORDER BY commenttime DESC,replytime DESC 

可以看到評論id為1和2的評論都有3條回復，這時對評論分頁直接用limit，比如limit 2,就取不到評論id為1的評論，然后mybatis自動分組后就只有一條評論。

解決方法是外面不用limit,在where條件中，對articlecomment_id使用in子查詢，在in子查詢里面用limit，取出指定limit的滿足條件還沒有外連接的評論的articlecomment_id。

表數據

        SELECT articlecomment.articlecomment_id,articlecomment.commenttime,articlecomment.commentcontent,articlecomment.id AS commentuser_id
        ,articlereply.articlereply_id,articlereply.replytime,articlereply.replycontent,articlereply.id AS replyuser_id
        ,u1.name AS comment_user,u2.name AS reply_user FROM articlecomment 
        LEFT JOIN articlereply ON articlereply.comment_id=articlecomment.articlecomment_id INNER JOIN USER AS u1 ON u1.id=articlecomment.id 
        LEFT JOIN USER AS u2 ON u2.id=articlereply.id WHERE articlecomment.articlecomment_id IN(SELECT articlecomment1.articlecomment_id 
        FROM articlecomment AS articlecomment1 WHERE articlecomment1.article_id=1 ORDER BY articlecomment1.articlecomment_id DESC LIMIT 2
        ) ORDER BY articlecomment.articlecomment_id DESC,replytime DESC

這時會顯示錯誤，This version of MySQL doesn't yet support 'LIMIT & IN/ALL/ANY/SOME subquery'。

很容易搜到鳥哥的這篇MySQL也真是讓人郁悶(關於子查詢中使用limit)。在外面加一層就可以了。

        SELECT articlecomment.articlecomment_id,articlecomment.commenttime,articlecomment.commentcontent,articlecomment.id AS commentuser_id
        ,articlereply.articlereply_id,articlereply.replytime,articlereply.replycontent,articlereply.id AS replyuser_id
        ,u1.name AS comment_user,u2.name AS reply_user FROM articlecomment 
        LEFT JOIN articlereply ON articlereply.comment_id=articlecomment.articlecomment_id INNER JOIN USER AS u1 ON u1.id=articlecomment.id 
        LEFT JOIN USER AS u2 ON u2.id=articlereply.id WHERE articlecomment.articlecomment_id IN(SELECT articlecomment1.articlecomment_id 
        FROM (SELECT * FROM articlecomment AS articlecomment2 WHERE articlecomment2.article_id=1 ORDER BY articlecomment2.articlecomment_id DESC LIMIT 2) 
        AS articlecomment1 ) ORDER BY articlecomment.articlecomment_id DESC,replytime DESC