limit 优化测试

user 表共有37条记录

1.select * 无 where 条件 

mysql> explain select * from user limit 29,7 \G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: user
type: ALL
possible_keys: NULL
key: NULL
key_len: NULL
ref: NULL
rows: 37
Extra:

2.select * 有 where 条件

mysql> explain select * from user where id > 29 limit 0,7 \G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: user
type: range
possible_keys: PRIMARY
key: PRIMARY
key_len: 4
ref: NULL
rows: 8
Extra: Using where

3.select col_name 有where 条件

mysql> explain select age from user where id > 29 limit 0,7 \G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: user
type: range
possible_keys: PRIMARY
key: PRIMARY
key_len: 4
ref: NULL
rows: 8
Extra: Using where

实际查询耗时对比

mysql> select * from buy_keywords limit 50000,10;
//省略数据显示
10 rows in set (0.16 sec)

mysql> select * from buy_keywords where id > 50000 limit 0,10;
//省略数据显示
10 rows in set (0.03 sec)






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