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问题一：1.有什么可视化的，能够特别直观的分析SQL语句性能的工具？
问题二：
select * limit offset,amount; select * where id between offset and offset+amount; select * where id > offset limit amount;
以上三个SQL语句，哪个性能更佳呢？项目中我们一般用的好像是limit a b 这样的吧，性能又如何呢？
认证0级讲师
http://www.cnblogs.com/RunFor...
explain
根据上面提到的explain去比较，就可以得出结果了
mysql> explain select * from users limit 1000,20; +----+-------------+-------+------+---------------+------+---------+------+--------+-------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+------+--------+-------+ | 1 | SIMPLE | users | ALL | NULL | NULL | NULL | NULL | 169847 | | +----+-------------+-------+------+---------------+------+---------+------+--------+-------+ 1 row in set (0.00 sec)
mysql> explain select * from users where uid>1000 limit 20; +----+-------------+-------+-------+---------------+---------+---------+------+-------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+-------+---------------+---------+---------+------+-------+-------------+ | 1 | SIMPLE | users | range | PRIMARY | PRIMARY | 4 | NULL | 84923 | Using where | +----+-------------+-------+-------+---------------+---------+---------+------+-------+-------------+ 1 row in set (0.00 sec)
mysql> explain select * from users where uid between 1000 and 1020; +----+-------------+-------+-------+---------------+---------+---------+------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+-------+---------------+---------+---------+------+------+-------------+ | 1 | SIMPLE | users | range | PRIMARY | PRIMARY | 4 | NULL | 1 | Using where | +----+-------------+-------+-------+---------------+---------+---------+------+------+-------------+ 1 row in set (0.00 sec)
explain +1还有，你这3条SQL表达的都不是一个意思，所以无可比性。
参考：https://mp.weixin.qq.com/s?__...
select * limit offset,amount;select * where id between offset and offset+amount;select * where id > offset limit amount; 这条性能最佳为何？因为id比较走了索引，如果id没有索引，还可以加索引，请记住，select判断性能佳不佳 首先去看下自己的where条件有没有可能走索引，如果自己的几种方案都走了索引，那么再用explain去具体看下到底哪些语句性能最佳
后两个要优于第一个
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
http://www.cnblogs.com/RunFor...
explain
根据上面提到的explain去比较，就可以得出结果了
explain +1
还有，你这3条SQL表达的都不是一个意思，所以无可比性。
参考：https://mp.weixin.qq.com/s?__...
select * limit offset,amount;
select * where id between offset and offset+amount;
select * where id > offset limit amount; 这条性能最佳
为何？因为id比较走了索引，如果id没有索引，还可以加索引，请记住，select判断性能佳不佳 首先去看下自己的where条件有没有可能走索引，如果自己的几种方案都走了索引，那么再用explain去具体看下到底哪些语句性能最佳
后两个要优于第一个