本篇内容介绍了“MySQL内存表的缺点是什么”的有关知识，在实际案例的操作过程中，不少人都会遇到这样的困境，接下来就让小编带领大家学习一下如何处理这些情况吧！希望大家仔细阅读，能够学有所成！
CREATETABLE`mem_test`(`id`int(10)unsignednOTNULLDEFAULT'0',`name`varchar(10)DEFAULTNULL,`first`varchar(10)DEFAULTNULL,PRIMARYKEY(`id`),KEY`NewIndex1`(`name`,`first`))ENGINE=MEMORY;CREATETABLE`innodb_test`(`id`int(10)unsignednOTNULLDEFAULT'0',`name`varchar(10)DEFAULTNULL,`first`varchar(10)DEFAULTNULL,PRIMARYKEY(`id`),KEY`NewIndex1`(`name`,`first`))ENGINE=InnoDB;
如：
1：在=或者<=>情况下，飞快，但是在如<或>情况下，他是不使用索引
MysqL--chinastor.com-root@localhost:17db07:33:45>>explainselect*frommem_testwhereid>3;+----+-------------+----------+------+---------------+------+---------+------+------+-------------+|id|select_type|table|type|possible_keys|key|key_len|ref|rows|Extra|+----+-------------+----------+------+---------------+------+---------+------+------+-------------+|1|SIMPLE|mem_test|ALL|PRIMARY|NULL|NULL|NULL|15|Usingwhere|+----+-------------+----------+------+---------------+------+---------+------+------+-------------+1rowinset(0.00sec)MysqL--chinastor.com-root@localhost:17db07:33:49>>explainselect*frominnodb_testwhereid>3;+----+-------------+-------------+-------+---------------+---------+---------+------+------+-------------+|id|select_type|table|type|possible_keys|key|key_len|ref|rows|Extra|+----+-------------+-------------+-------+---------------+---------+---------+------+------+-------------+|1|SIMPLE|innodb_test|range|PRIMARY|PRIMARY|4|NULL|7|Usingwhere|+----+-------------+-------------+-------+---------------+---------+---------+------+------+-------------+1rowinset(0.00sec)
2：不能用在orderby情况下来提高速度
MysqL--chinastor.com-root@localhost:17db07:33:55>>explainselect*frominnodb_testorderbyid;+----+-------------+-------------+-------+---------------+---------+---------+------+------+-------+|id|select_type|table|type|possible_keys|key|key_len|ref|rows|Extra|+----+-------------+-------------+-------+---------------+---------+---------+------+------+-------+|1|SIMPLE|innodb_test|index|NULL|PRIMARY|4|NULL|15||+----+-------------+-------------+-------+---------------+---------+---------+------+------+-------+1rowinset(0.00sec)MysqL--chinastor.com-root@localhost:17db07:34:27>>explainselect*frommem_testorderbyid;+----+-------------+----------+------+---------------+------+---------+------+------+----------------+|id|select_type|table|type|possible_keys|key|key_len|ref|rows|Extra|+----+-------------+----------+------+---------------+------+---------+------+------+----------------+|1|SIMPLE|mem_test|ALL|NULL|NULL|NULL|NULL|15|Usingfilesort|+----+-------------+----------+------+---------------+------+---------+------+------+----------------+1rowinset(0.00sec)
MysqL内存表的弊端有什么
3：不能确定俩值之间有多少行
MysqL--chinastor.com-root@localhost:17db07:37:14>>explainselectcount(1)frommem_testwhereid>3andid<6;+----+-------------+----------+------+---------------+------+---------+------+------+-------------+|id|select_type|table|type|possible_keys|key|key_len|ref|rows|extra|+----+-------------+----------+------+---------------+------+---------+------+------+-------------+|1|simple|mem_test|all|primary|null|null|null|20|usingwhere|+----+-------------+----------+------+---------------+------+---------+------+------+-------------+1rowinset(0.00sec)MysqL--chinastor.com-root@localhost:17db07:40:35>>explainselectcount(1)frominnodb_testwhereid>3andid<6;+----+-------------+-------------+-------+---------------+---------+---------+------+------+--------------------------+|id|select_type|table|type|possible_keys|key|key_len|ref|rows|extra|+----+-------------+-------------+-------+---------------+---------+---------+------+------+--------------------------+|1|simple|innodb_test|range|primary|primary|4|null|1|usingwhere;usingindex|+----+-------------+-------------+-------+---------------+---------+---------+------+------+--------------------------+1rowinset(0.00sec) localhost:17db07:37:07="">>explainselect*frominnodb_testwherename='b';+----+-------------+-------------+------+---------------+-----------+---------+-------+------+--------------------------+|id|select_type|table|type|possible_keys|key|key_len|ref|rows|Extra|+----+-------------+-------------+------+---------------+-----------+---------+-------+------+--------------------------+|1|SIMPLE|innodb_test|ref|NewIndex1|NewIndex1|33|const|8|Usingwhere;Usingindex|+----+-------------+-------------+------+---------------+-----------+---------+-------+------+--------------------------+1rowinset(0.00sec)MysqL--chinastor.com-root@localhost:17db07:37:10>>explainselect*frommem_testwherename='b';+----+-------------+----------+------+---------------+------+---------+------+------+-------------+|id|select_type|table|type|possible_keys|key|key_len|ref|rows|Extra|+----+-------------+----------+------+---------------+------+---------+------+------+-------------+|1|SIMPLE|mem_test|ALL|NewIndex1|NULL|NULL|NULL|20|Usingwhere|+----+-------------+----------+------+---------------+------+---------+------+------+-------------+
当然内存表也可以手动添加btree
CREATEINDEXBTREE_indexUSINGBTREEonmem_test(name,first)MysqL--chinastor.com-root@localhost:17db03:36:41>>explainselect*frommem_testwherename='b';+----+-------------+----------+------+-----------------------+-------------+---------+-------+------+-------------+|id|select_type|table|type|possible_keys|key|key_len|ref|rows|Extra|+----+-------------+----------+------+-----------------------+-------------+---------+-------+------+-------------+|1|SIMPLE|mem_test|ref|NewIndex1,BTREE_index|BTREE_index|33|const|9|Usingwhere|+----+-------------+----------+------+-----------------------+-------------+---------+-------+------+-------------+1rowinset(0.00sec)
哈哈，它也用到索引了。
所以要选择合适的存储引擎至关重要。
“MysqL内存表的缺点是什么”的内容就介绍到这里了，感谢大家的阅读。如果想了解更多行业相关的知识可以关注编程之家网站，小编将为大家输出更多高质量的实用文章！
