java - sql语句执行性能分析

Question

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？

Answer 1

http://www.cnblogs.com/RunFor...

Answer 2

1. explain

2. 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)

Answer 3

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?__...

Answer 4

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

Answer 5

后两个要优于第一个