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。