这篇文章将为大家详细讲解有关关系型数据库在龙腾科技字段上作喜欢操作的消耗是怎样的，文章内容质量较高，因此小编分享给大家做个参考，希望大家阅读完这篇文章后对相关知识有一定的了解。
# Mysql 5140 @ RHEL 5u4 X86_64
# 先提供一些表的信息：
===================================================================
root @ 127。0 .0 .1 : TRAC _ apsara 17:18:46显示创建表格wiki G
*************************** 1.行**************************
表：维基
创建表格：创建表格` wiki `(
` name` longtext COLLATE utf8_bin，
` version` int(11) DEFAULT NULL，
` time` bigint(20) DEFAULT NULL，
`作者` longtext COLLATE utf8_bin，
` ipnr` longtext COLLATE utf8_bin，
` text` longtext COLLATE utf8_bin，
` comment `长文本COLLATE utf8 _ bin，
` readonly ' int(11)DEFAULT NULL，
KEY `wiki_time_idx` (`time `)，
KEY `name_ver_ind` (`name`(200)，` version `)
)ENGINE=Innodb DEFAULT CHARSET=utf 8 COLLATE=utf 8 _ bin
一行一组(0.00秒)
root @ 127。0 .0 .1 : TRAC _ apsara 17:19:04从维基网中选择计数(*)；
-
|计数(*) |
-
| 76514 |
-
一行一组(0.03秒)
root @ 127。0 .0 .1 : TRAC _ apsara 17:19:08从维基网中选择计数(不同的名称)；
-
|计数（不同的名称)|
-
| 40369 |
-
一行一组(0.59秒)
root @ 127。0 .0 .1 : TRAC _ apsara 17:19:21显示像innodb_buffer% '这样的变量；
- -
|变量名|值|
- -
| innodb _ buffer _ pool _ size | 1073741824 |
- -
一行一组(0.00秒)
root @ 127。0 .0 .1 : TRAC _ apsara 17:21:08像“维基”G一样显示表状态
*************************** 1.行**************************
名称：维基
发动机：
版本： 10
行格式：压缩
排
s: 336009
Avg_row_length: 4458
Data_length: 1498120192
Max_data_length: 0
Index_length: 10551296
Data_free: 7340032
Auto_increment: NULL
Create_time: 2010-09-29 14:49:20
Update_time: NULL
Check_time: NULL
Collation: utf8_bin
Checksum: NULL
Create_options:
Comment:
1 row in set (0.01 sec)
===================================================================
#下面我们来看一下SQL和数据：
## SQL1 :
SELECT w1.name,w1.time,w1.author,w1.text
FROM wiki w1,
(SELECT name,max(version) AS ver FROM wiki GROUP BY name) w2
WHERE w1.version = w2.ver AND w1.name = w2.name
AND (w1.name LIKE '%RpcRequestPtr%' ESCAPE '/'
OR w1.author LIKE '%RpcRequestPtr%' ESCAPE '/'
OR w1.text LIKE '%RpcRequestPtr%' ESCAPE '/'
);
## SQL2 :
SELECT w1.name,w1.time,w1.author,w1.text
FROM wiki w1,
(SELECT name,max(version) AS ver FROM wiki GROUP BY name) w2
WHERE w1.version = w2.ver AND w1.name = w2.name
AND (w1.name LIKE '%RpcRequestPtr%' ESCAPE '/'
OR w1.author LIKE '%RpcRequestPtr%' ESCAPE '/'
###### OR w1.text LIKE '%RpcRequestPtr%' ESCAPE '/'
);
两个SQL仅一个WHERE条件之差。
root@127.0.0.1 : trac_apsara 17:24:08> explain SELECT w1.name,w1.time,w1.author,w1.text
-> FROM wiki w1,
-> (SELECT name,max(version) AS ver FROM wiki GROUP BY name) w2
-> WHERE w1.version = w2.ver AND w1.name = w2.name
-> AND (w1.name LIKE '%RpcRequestPtr%' ESCAPE '/'
-> OR w1.author LIKE '%RpcRequestPtr%' ESCAPE '/'
-> OR w1.text LIKE '%RpcRequestPtr%' ESCAPE '/'
-> );
+----+-------------+------------+------+---------------+--------------+---------+----------------+--------+---------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+------------+------+---------------+--------------+---------+----------------+--------+---------------------------------+
| 1 | PRIMARY || ALL | NULL | NULL | NULL | NULL | 40369 | |
| 1 | PRIMARY | w1 | ref | name_ver_ind | name_ver_ind | 608 | w2.name,w2.ver | 3 | Using where |
| 2 | DERIVED | wiki | ALL | NULL | NULL | NULL | NULL | 445724 | Using temporary; Using filesort |
+----+-------------+------------+------+---------------+--------------+---------+----------------+--------+---------------------------------+
3 rows in set (1.04 sec)
root@127.0.0.1 : trac_apsara 17:22:26> explain SELECT w1.name,w1.time,w1.author,w1.text
-> FROM wiki w1,
-> (SELECT name,max(version) AS ver FROM wiki GROUP BY name) w2
-> WHERE w1.version = w2.ver AND w1.name = w2.name
-> AND (w1.name LIKE '%RpcRequestPtr%' ESCAPE '/'
-> OR w1.author LIKE '%RpcRequestPtr%' ESCAPE '/'
-> # OR w1.text LIKE '%RpcRequestPtr%' ESCAPE '/'
-> );
+----+-------------+------------+------+---------------+--------------+---------+----------------+--------+---------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+------------+------+---------------+--------------+---------+----------------+--------+---------------------------------+
| 1 | PRIMARY || ALL | NULL | NULL | NULL | NULL | 40369 | |
| 1 | PRIMARY | w1 | ref | name_ver_ind | name_ver_ind | 608 | w2.name,w2.ver | 3 | Using where |
| 2 | DERIVED | wiki | ALL | NULL | NULL | NULL | NULL | 445724 | Using temporary; Using filesort |
+----+-------------+------------+------+---------------+--------------+---------+----------------+--------+---------------------------------+
3 rows in set (1.03 sec)
### 从执行计划来看，两个SQL一模一样； 处理的行数也是一样的；
root@127.0.0.1 : trac_apsara 17:25:39> reset query cache ;
Query OK, 0 rows affected (0.00 sec)
root@127.0.0.1 : trac_apsara 17:25:52> SELECT w1.name,w1.time,w1.author,w1.text
-> FROM wiki w1,
-> (SELECT name,max(version) AS ver FROM wiki GROUP BY name) w2
-> WHERE w1.version = w2.ver AND w1.name = w2.name
-> AND (w1.name LIKE '%RpcRequestPtr%' ESCAPE '/'
-> OR w1.author LIKE '%RpcRequestPtr%' ESCAPE '/'
-> # OR w1.text LIKE '%RpcRequestPtr%' ESCAPE '/'
-> );
Empty set (1.31 sec)
root@127.0.0.1 : trac_apsara 17:26:12> reset query cache ;
Query OK, 0 rows affected (0.00 sec)
root@127.0.0.1 : trac_apsara 17:26:15> SELECT w1.name,w1.time,w1.author,w1.text
-> FROM wiki w1,
-> (SELECT name,max(version) AS ver FROM wiki GROUP BY name) w2
-> WHERE w1.version = w2.ver AND w1.name = w2.name
-> AND (w1.name LIKE '%RpcRequestPtr%' ESCAPE '/'
-> OR w1.author LIKE '%RpcRequestPtr%' ESCAPE '/'
-> OR w1.text LIKE '%RpcRequestPtr%' ESCAPE '/'
-> );
13 rows in set (3.50 sec)
## 从执行时间来看,
## SQL1 : 3.50 sec , SQL2: 1.31 sec
## 从这里我们基本可以判断出来，MYSQL 用了 2.19 sec 在内存中处理40369次TEXT字段的LIKE模糊查询操作；
## 而从WIKI表INDEX查询40369次，却只用了1.31秒（可能更少），当然数据已经在CACHE里。
## 我们以后做SQL可要注意了。不光是读硬盘会消耗时间，在内存中的LIKE模糊查询操作，也很费时间；
关于Mysql在LONGTEXT字段上作like操作的消耗是怎样的就分享到这里了，希望
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