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  • mysql分页

    mysql分页

    详细参考:https://blog.csdn.net/justlpf/article/details/81507586

    0、limit:最基本的方式(最差的方式)

    SELECT * FROM articles WHERE category_id = 123 ORDER BY id LIMIT 50, 10

    1、limit:尽量给出查询的大致范围

    SELECT c1,c2,cn... FROM table WHERE id>=20000 LIMIT 10;

    2、子查询法

    SELECT c1,c2,cn... FROM table WHERE id>=
    (SELECT id FROM table LIMIT 20000,1) LIMIT 10;

    3、JOIN分页

    优化前SQL:
    
    SELECT c1,c2,cn... FROM member ORDER BY last_active LIMIT 50,5
    优化后SQL:
    
    SELECT c1, c2, cn .. .
    FROM member t1
    INNER JOIN (SELECT member_id FROM member ORDER BY last_active LIMIT 50, 5) t2
    on t1.
    member_id =t2.member_id
    -- USING (member_id)

    join分页
    -- 1
    SELECT
    * FROM `content` AS t1 JOIN (SELECT id FROM `content` ORDER BY id desc LIMIT ".($page-1)*$pagesize.", 1) AS t2 WHERE t1.id <= t2.id ORDER BY t1.id desc LIMIT $pagesize;

    -- 2
    SELECT * FROM product a JOIN (select id from product limit 866613, 20) b ON a.ID = b.id
    
    
    
     

    分别在于,优化前的SQL需要更多I/O浪费,因为先读索引,再读数据,然后抛弃无需的行。而优化后的SQL(子查询那条)只读索引(Cover index)就可以了,然后通过member_id读取需要的列。

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  • 原文地址:https://www.cnblogs.com/gered/p/10826936.html
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