MySQL 主键范围查找问题
背景：
今天遇到一个主键范围查找的情况：
select ... from tb left join tb1 on ... where tb.id between 0 and 10000
id是主键，每次取10000。上面的这个查询id范围越往后面消耗的时间越久。通过id自增主键去查找数据应该不会出现这个现象的。以前都没有注意这个奇怪的现象，现在就好好分析下。
知识点：
索引的根节点到子节点的距离是一样的，根节点包含指向子节点的指针，存储引擎通过指针来查找数据。所以通过索引查找他们的消耗是一样的。
测试：
1：SQL结构：
explain select sql_no_cache post.id, post.root, post.boardId, post.postTime, post.subject, post.file, body.body, post.userId, post.click, post.child, post.type, post.rating, post.votes, topic.approved, topic.archived, topic.reply, user.status from j_post as post left join j_post_body as body on post.id = body.id left join j_topic as topic on post.id=topic.id left join j_user as user on user.id=post.userId where post.id between 1090000 and 1100000;
+----+-------------+-------+--------+---------------+---------+---------+------------------+-------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+--------+---------------+---------+---------+------------------+-------+-------------+
| 1 | SIMPLE | post | range | PRIMARY | PRIMARY | 4 | NULL | 17876 | Using where |
| 1 | SIMPLE | body | eq_ref | PRIMARY | PRIMARY | 4 | jute.post.id | 1 | |
| 1 | SIMPLE | topic | eq_ref | PRIMARY | PRIMARY | 4 | jute.post.id | 1 | |
| 1 | SIMPLE | user | eq_ref | PRIMARY | PRIMARY | 4 | jute.post.userId | 1 | |
+----+-------------+-------+--------+---------------+---------+---------+------------------+-------+-------------+
执行的状况：
1090000 and 1100000
>show profile cpu,block io for query 1;
+----------------------+----------+----------+------------+--------------+---------------+
| Status | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |
+----------------------+----------+----------+------------+--------------+---------------+
| starting | 0.000156 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000008 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000004 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000004 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000008 | 0.000000 | 0.000000 | 0 | 0 |
| Opening tables | 0.000062 | 0.000000 | 0.000000 | 0 | 0 |
| System lock | 0.000017 | 0.000000 | 0.000000 | 0 | 0 |
| init | 0.000068 | 0.000000 | 0.000000 | 0 | 0 |
| optimizing | 0.000021 | 0.000000 | 0.000000 | 0 | 0 |
| statistics | 0.001326 | 0.004001 | 0.000000 | 0 | 0 |
| preparing | 0.000030 | 0.000000 | 0.000000 | 0 | 0 |
| executing | 0.000006 | 0.000000 | 0.000000 | 0 | 0 |
| Sending data | 0.640303 | 0.384024 | 0.028001 | 0 | 0 |
| end | 0.000020 | 0.000000 | 0.000000 | 0 | 0 |
| query end | 0.000008 | 0.000000 | 0.000000 | 0 | 0 |
| closing tables | 0.000016 | 0.000000 | 0.000000 | 0 | 0 |
| freeing items | 0.000026 | 0.000000 | 0.000000 | 0 | 0 |
| logging slow query | 0.000006 | 0.000000 | 0.000000 | 0 | 0 |
| cleaning up | 0.000008 | 0.000000 | 0.000000 | 0 | 0 |
+----------------------+----------+----------+------------+--------------+---------------+
19 rows in set (0.01 sec) 21000000 and 21010000
>show profile cpu,block io for query 2;
+----------------------+----------+----------+------------+--------------+---------------+
| Status | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |
+----------------------+----------+----------+------------+--------------+---------------+
| starting | 0.000161 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000010 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000004 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000005 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000008 | 0.000000 | 0.000000 | 0 | 0 |
| Opening tables | 0.000042 | 0.000000 | 0.000000 | 0 | 0 |
| System lock | 0.000015 | 0.000000 | 0.000000 | 0 | 0 |
| init | 0.000065 | 0.000000 | 0.000000 | 0 | 0 |
| optimizing | 0.000022 | 0.000000 | 0.000000 | 0 | 0 |
| statistics | 0.017431 | 0.000000 | 0.000000 | 144 | 0 |
| preparing | 0.000031 | 0.000000 | 0.000000 | 0 | 0 |
| executing | 0.000006 | 0.000000 | 0.000000 | 0 | 0 |
| Sending data | 3.228074 | 0.696043 | 0.164010 | 45936 | 0 |
| end | 0.000020 | 0.000000 | 0.000000 | 0 | 0 |
| query end | 0.000009 | 0.000000 | 0.000000 | 0 | 0 |
| closing tables | 0.000018 | 0.000000 | 0.000000 | 0 | 0 |
| freeing items | 0.000052 | 0.000000 | 0.000000 | 0 | 0 |
| logging slow query | 0.000008 | 0.000000 | 0.000000 | 0 | 0 |
| cleaning up | 0.000009 | 0.000000 | 0.000000 | 0 | 0 |
+----------------------+----------+----------+------------+--------------+---------------+
19 rows in set (0.01 sec) 26000000 and 26010000
>show profile cpu,block io for query 3;
+----------------------+----------+----------+------------+--------------+---------------+
| Status | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |
+----------------------+----------+----------+------------+--------------+---------------+
| starting | 0.000146 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000008 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000004 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000004 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000007 | 0.000000 | 0.000000 | 0 | 0 |
| Opening tables | 0.000042 | 0.000000 | 0.000000 | 0 | 0 |
| System lock | 0.000015 | 0.000000 | 0.000000 | 0 | 0 |
| init | 0.000065 | 0.000000 | 0.000000 | 0 | 0 |
| optimizing | 0.000021 | 0.000000 | 0.000000 | 0 | 0 |
| statistics | 0.013855 | 0.004000 | 0.000000 | 392 | 0 |
| preparing | 0.000064 | 0.000000 | 0.000000 | 0 | 0 |
| executing | 0.000009 | 0.000000 | 0.000000 | 0 | 0 |
| Sending data | 4.075430 | 0.676042 | 0.140009 | 82288 | 0 |
| end | 0.000021 | 0.000000 | 0.000000 | 0 | 0 |
| query end | 0.000010 | 0.000000 | 0.000000 | 0 | 0 |
| closing tables | 0.000019 | 0.000000 | 0.000000 | 0 | 0 |
| freeing items | 0.000050 | 0.000000 | 0.000000 | 0 | 0 |
| logging slow query | 0.000007 | 0.000000 | 0.000000 | 0 | 0 |
| cleaning up | 0.000009 | 0.000000 | 0.000000 | 0 | 0 |
+----------------------+----------+----------+------------+--------------+---------------+
19 rows in set (0.03 sec) 6000000 and 6010000
>show profile cpu,block io for query 4;
+----------------------+----------+----------+------------+--------------+---------------+
| Status | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |
+----------------------+----------+----------+------------+--------------+---------------+
| starting | 0.000164 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000008 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000004 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000005 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000008 | 0.000000 | 0.000000 | 0 | 0 |
| Opening tables | 0.000041 | 0.000000 | 0.000000 | 0 | 0 |
| System lock | 0.000015 | 0.000000 | 0.000000 | 0 | 0 |
| init | 0.000064 | 0.000000 | 0.000000 | 0 | 0 |
| optimizing | 0.000021 | 0.000000 | 0.000000 | 0 | 0 |
| statistics | 0.013467 | 0.004000 | 0.000000 | 392 | 0 |
| preparing | 0.000032 | 0.000000 | 0.000000 | 0 | 0 |
| executing | 0.000006 | 0.000000 | 0.000000 | 0 | 0 |
| Sending data | 1.345275 | 0.476030 | 0.084005 | 19848 | 0 |
| end | 0.000021 | 0.000000 | 0.000000 | 0 | 0 |
| query end | 0.000042 | 0.000000 | 0.000000 | 0 | 0 |
| closing tables | 0.000022 | 0.000000 | 0.000000 | 0 | 0 |
| freeing items | 0.000058 | 0.000000 | 0.000000 | 0 | 0 |
| logging slow query | 0.000015 | 0.000000 | 0.000000 | 0 | 0 |
| cleaning up | 0.000012 | 0.000000 | 0.000000 | 0 | 0 |
+----------------------+----------+----------+------------+--------------+---------------+
19 rows in set (0.02 sec) 27000000 and 27010000
>show profile cpu,block io for query 5;
+----------------------+----------+----------+------------+--------------+---------------+
| Status | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |
+----------------------+----------+----------+------------+--------------+---------------+
| starting | 0.000144 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000007 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000004 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000004 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000007 | 0.000000 | 0.000000 | 0 | 0 |
| Opening tables | 0.000041 | 0.000000 | 0.000000 | 0 | 0 |
| System lock | 0.000016 | 0.000000 | 0.000000 | 0 | 0 |
| init | 0.000065 | 0.000000 | 0.000000 | 0 | 0 |
| optimizing | 0.000021 | 0.000000 | 0.000000 | 0 | 0 |
| statistics | 0.011399 | 0.000000 | 0.000000 | 208 | 0 |
| preparing | 0.000032 | 0.000000 | 0.000000 | 0 | 0 |
| executing | 0.000006 | 0.000000 | 0.000000 | 0 | 0 |
| Sending data | 3.157346 | 0.616038 | 0.176011 | 71840 | 0 |
| end | 0.000021 | 0.000000 | 0.000000 | 0 | 0 |
| query end | 0.000054 | 0.000000 | 0.000000 | 0 | 0 |
| closing tables | 0.000020 | 0.000000 | 0.000000 | 0 | 0 |
| freeing items | 0.000056 | 0.000000 | 0.000000 | 0 | 0 |
| logging slow query | 0.000007 | 0.000000 | 0.000000 | 0 | 0 |
| cleaning up | 0.000027 | 0.000000 | 0.000000 | 0 | 0 |
+----------------------+----------+----------+------------+--------------+---------------+
19 rows in set (0.02 sec)
从上面的结果可以看出越往后，消耗的时间越久。
这个和知识点里说的不一样，为什么出现这个情况？先从另一方面看：上面是连表查询，很可能出现问题的不是使用主键id的这个表。那就开始用单表看看，会是怎么样的情况。
2：SQL结构
explain select sql_no_cache post.id, post.root, post.boardId, post.postTime, post.subject, post.file, post.userId, post.click, post.child, post.type, post.rating, post.votes from jute_post as post where post.id between 1090000 and 1100000;
+----+-------------+-------+-------+---------------+---------+---------+------+-------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+-------+---------------+---------+---------+------+-------+-------------+
| 1 | SIMPLE | post | range | PRIMARY | PRIMARY | 4 | NULL | 17876 | Using where |
+----+-------------+-------+-------+---------------+---------+---------+------+-------+-------------+
执行状况：
1090000 and 1100000
+----------------------+----------+----------+------------+--------------+---------------+
| Status | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |
+----------------------+----------+----------+------------+--------------+---------------+
| starting | 0.000164 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000013 | 0.000000 | 0.000000 | 0 | 0 |
| Opening tables | 0.174908 | 0.012001 | 0.004000 | 1720 | 0 |
| System lock | 0.000046 | 0.000000 | 0.000000 | 0 | 0 |
| init | 0.000066 | 0.000000 | 0.000000 | 0 | 0 |
| optimizing | 0.000033 | 0.000000 | 0.000000 | 0 | 0 |
| statistics | 0.001264 | 0.004000 | 0.000000 | 0 | 0 |
| preparing | 0.000040 | 0.000000 | 0.000000 | 0 | 0 |
| executing | 0.000007 | 0.000000 | 0.000000 | 0 | 0 |
| Sending data | 0.057492 | 0.052004 | 0.004000 | 16 | 0 |
| end | 0.000026 | 0.000000 | 0.000000 | 0 | 0 |
| query end | 0.000010 | 0.000000 | 0.000000 | 0 | 0 |
| closing tables | 0.000013 | 0.000000 | 0.000000 | 0 | 0 |
| freeing items | 0.000023 | 0.000000 | 0.000000 | 0 | 0 |
| logging slow query | 0.000005 | 0.000000 | 0.000000 | 0 | 0 |
| cleaning up | 0.000006 | 0.000000 | 0.000000 | 0 | 0 |
+----------------------+----------+----------+------------+--------------+---------------+ 21000000 and 21010000
+----------------------+----------+----------+------------+--------------+---------------+
| Status | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |
+----------------------+----------+----------+------------+--------------+---------------+
| starting | 0.000101 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000011 | 0.000000 | 0.000000 | 0 | 0 |
| Opening tables | 0.000025 | 0.000000 | 0.000000 | 0 | 0 |
| System lock | 0.000029 | 0.000000 | 0.000000 | 0 | 0 |
| init | 0.000044 | 0.000000 | 0.000000 | 0 | 0 |
| optimizing | 0.000013 | 0.000000 | 0.000000 | 0 | 0 |
| statistics | 0.007977 | 0.000000 | 0.000000 | 32 | 0 |
| preparing | 0.000024 | 0.000000 | 0.000000 | 0 | 0 |
| executing | 0.000005 | 0.000000 | 0.000000 | 0 | 0 |
| Sending data | 0.083919 | 0.068004 | 0.004001 | 288 | 0 |
| end | 0.000021 | 0.000000 | 0.000000 | 0 | 0 |
| query end | 0.000009 | 0.000000 | 0.000000 | 0 | 0 |
| closing tables | 0.000012 | 0.000000 | 0.000000 | 0 | 0 |
| freeing items | 0.000021 | 0.000000 | 0.000000 | 0 | 0 |
| logging slow query | 0.000005 | 0.000000 | 0.000000 | 0 | 0 |
| cleaning up | 0.000006 | 0.000000 | 0.000000 | 0 | 0 |
+----------------------+----------+----------+------------+--------------+---------------+ 26000000 and 26010000
+----------------------+----------+----------+------------+--------------+---------------+
| Status | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |
+----------------------+----------+----------+------------+--------------+---------------+
| starting | 0.000102 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000011 | 0.000000 | 0.000000 | 0 | 0 |
| Opening tables | 0.000025 | 0.000000 | 0.000000 | 0 | 0 |
| System lock | 0.000015 | 0.000000 | 0.000000 | 0 | 0 |
| init | 0.000043 | 0.000000 | 0.000000 | 0 | 0 |
| optimizing | 0.000012 | 0.000000 | 0.000000 | 0 | 0 |
| statistics | 0.001315 | 0.000000 | 0.000000 | 0 | 0 |
| preparing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 |
| executing | 0.000005 | 0.000000 | 0.000000 | 0 | 0 |
| Sending data | 0.083872 | 0.068004 | 0.004000 | 48 | 0 |
| end | 0.000021 | 0.000000 | 0.000000 | 0 | 0 |
| query end | 0.000008 | 0.000000 | 0.000000 | 0 | 0 |
| closing tables | 0.000013 | 0.000000 | 0.000000 | 0 | 0 |
| freeing items | 0.000024 | 0.000000 | 0.000000 | 0 | 0 |
| logging slow query | 0.000011 | 0.000000 | 0.000000 | 0 | 0 |
| cleaning up | 0.000006 | 0.000000 | 0.000000 | 0 | 0 |
+----------------------+----------+----------+------------+--------------+---------------+ 6000000 and 6010000
+----------------------+----------+----------+------------+--------------+---------------+
| Status | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |
+----------------------+----------+----------+------------+--------------+---------------+
| starting | 0.000082 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000026 | 0.000000 | 0.000000 | 0 | 0 |
| Opening tables | 0.000021 | 0.000000 | 0.000000 | 0 | 0 |
| System lock | 0.000011 | 0.000000 | 0.000000 | 0 | 0 |
| init | 0.000032 | 0.000000 | 0.000000 | 0 | 0 |
| optimizing | 0.000009 | 0.000000 | 0.000000 | 0 | 0 |
| statistics | 0.000753 | 0.000000 | 0.004000 | 0 | 0 |
| preparing | 0.000017 | 0.000000 | 0.000000 | 0 | 0 |
| executing | 0.000004 | 0.000000 | 0.000000 | 0 | 0 |
| Sending data | 0.057981 | 0.036003 | 0.000000 | 40 | 0 |
| end | 0.000018 | 0.000000 | 0.000000 | 0 | 0 |
| query end | 0.000010 | 0.000000 | 0.000000 | 0 | 0 |
| closing tables | 0.000010 | 0.000000 | 0.000000 | 0 | 0 |
| freeing items | 0.007655 | 0.000000 | 0.000000 | 0 | 0 |
| logging slow query | 0.000007 | 0.000000 | 0.000000 | 0 | 0 |
| cleaning up | 0.000005 | 0.000000 | 0.000000 | 0 | 0 |
+----------------------+----------+----------+------------+--------------+---------------+ 27000000 and 27010000
+----------------------+----------+----------+------------+--------------+---------------+
| Status | Duration | CPU_user | CPU_system | Block_ops_in | Block_ops_out |
+----------------------+----------+----------+------------+--------------+---------------+
| starting | 0.000103 | 0.000000 | 0.000000 | 0 | 0 |
| checking permissions | 0.000011 | 0.000000 | 0.000000 | 0 | 0 |
| Opening tables | 0.000025 | 0.000000 | 0.000000 | 0 | 0 |
| System lock | 0.000015 | 0.000000 | 0.000000 | 0 | 0 |
| init | 0.000043 | 0.000000 | 0.000000 | 0 | 0 |
| optimizing | 0.000013 | 0.000000 | 0.000000 | 0 | 0 |
| statistics | 0.008353 | 0.000000 | 0.004001 | 8 | 0 |
| preparing | 0.000025 | 0.000000 | 0.000000 | 0 | 0 |
| executing | 0.000006 | 0.000000 | 0.000000 | 0 | 0 |
| Sending data | 0.071468 | 0.060004 | 0.004000 | 64 | 0 |
| end | 0.000022 | 0.000000 | 0.000000 | 0 | 0 |
| query end | 0.000009 | 0.000000 | 0.000000 | 0 | 0 |
| closing tables | 0.000013 | 0.000000 | 0.000000 | 0 | 0 |
| freeing items | 0.000020 | 0.000000 | 0.000000 | 0 | 0 |
| logging slow query | 0.000005 | 0.000000 | 0.000000 | 0 | 0 |
| cleaning up | 0.000006 | 0.000000 | 0.000000 | 0 | 0 |
+----------------------+----------+----------+------------+--------------+---------------+
发现上面执行时候消耗都差不多，验证了知识点里的内容。
总结：
上面的测试数据都是在磁盘上，没有预热的，所以和BP无关。通过1和2的测试对比得知：越往后越慢的问题在于Join，多表查出来不一样的时间，应该是跟数据在磁盘分布有关。id越往后越慢主要受到了其他几张关联表的影响。对于数据在磁盘上怎么分布的，有机会得去好好的学习下。
MySQL 主键范围查找问题的更多相关文章
- Mysql主键索引、唯一索引、普通索引、全文索引、组合索引的区别
原文:Mysql主键索引.唯一索引.普通索引.全文索引.组合索引的区别 Mysql索引概念: 说说Mysql索引,看到一个很少比如:索引就好比一本书的目录,它会让你更快的找到内容,显然目录(索引)并不 ...
- PowerDesigner 15设置mysql主键自动增长及基数
PowerDesigner 15设置mysql主键自动增长及基数 1.双击标示图,打开table properties->columns, 如图点击图标Customize Columns an ...
- MySQL主键设计
[TOC] 在项目过程中遇到一个看似极为基础的问题,但是在深入思考后还是引出了不少问题,觉得有必要把这一学习过程进行记录. MySQL主键设计原则 MySQL主键应当是对用户没有意义的. MySQL主 ...
- MYSQL主键自动增加的配置及auto_increment注意事项
文章一 原文地址: http://ej38.com/showinfo/mysql-202971.html 文章二: 点击转入第二篇文章 在数据库应用,我们经常要用到唯一编号.在MySQL中可通过字 ...
- 获得自动增长的MySQL主键
下面的脚本教您如何获得自动增长的MySQL主键,如果您对MySQL主键方面感兴趣的话,不妨一看,相信对您学习MySQL主键方面会有所启迪. import java.sql.Connection; im ...
- mysql主键设置成auto_increment时，进行并发性能測试出现主键反复Duplicate entry 'xxx' for key 'PRIMARY'
mysql主键设置成auto_increment时,进行并发性能測试出现主键反复Duplicate entry 'xxx' for key 'PRIMARY' 解决方法: 在my.cnf的[mysql ...
- Mysql 主键约束PrimaryKey
Mysql 主键约束Primary Key 今天来简单的讲一下主键约束. 假如有一张学生信息表,里面记录了学生的学号 ,姓名,成绩等,那么,会不会有两个学号相同的学生,答案肯定是否定的,如果有的话也只 ...
- mysql主键问题
版权声明:本文为博主原创文章,未经博主允许不得转载. https://blog.csdn.net/qq_22314145/article/details/80824660 MySQL主键 一. MyS ...
- MySQL主键与索引的区别和联系
MySQL主键与索引的区别和联系 关系数据库依赖于主键,它是数据库物理模式的基石.主键在物理层面上只有两个用途: 惟一地标识一行. 作为一个可以被外键有效引用的对象. 索引是一种特殊的文件(Inn ...
随机推荐
- 后缀.jar的是什么文件？
解压kafka 打开后是一堆.jar结尾的文件,那么后缀.jar的是什么文件? JAR 文件就是 Java Archive File,顾名思意,它的应用是与 Java 息息相关的,是 Java 的一种 ...
- openssh for windows安装
openssh for windows安装 2009-11-22 22:43:58 分类: WINDOWS 本文转自:http://blog.chinaunix.net/uid-7541208-id ...
- centos 安装 mysql5.7.9初始密码问题
mysql5.7.9在安装完成后会,root用户会产生一个不为空的初始密码,登陆mysql就会产生问题了,有必要修改一下登陆密码: 这是从网上找的一个方法,加以总结得出来的,亲测可以:# /etc/i ...
- 前端性能利器——dynatrace ajax edition
因为最近的工作跟性能分析有关系,所以写个小总结. 顺带推荐两个我常用的小工具: 1.文件对比工具beyond compare,非常好用,对比.修改很简单.当然我只是用的试用版本.google一下官网下 ...
- 免费的ER 设计软件调研
目标: 找到一个免费的ER 设计软件, 适合数据仓库项目开发. 结果: 经初步调研, Oracle的 SQL Developer Data Modeler基本满足需求. 但在功能和操作性等方面, 较P ...
- EF-Linq将查询结果转换为List<string>
List<int> id_list = new List<int>() { 1 };//测试数据...List<string> guid_list = (from ...
- Swift---TextView用法
1.TextView放在一个NSScrollView中,作为documentView存在. @IBOutlet weak var txtScrollView: NSScrollView! 2.在Tex ...
- Apache开发模块
输入perl Configure.pl 安装目录...\apache2.2 “httpd.exe” 生成apxs命令, apache2.2下build目录中的config_vars.mk文件 将CC ...
- rpc优化
1.刷文章列表的时候,发现调用总时间100ms ,其中调策略是花了60ms,一个开源的map方法dozer,组装bean要花40ms 2.redis的zounct方法,传 1和-1的时候有时候会返回0 ...
- JavaScript中的跨域
跨域是什么 跨域就是指从一个域名的网页去请求另一个域名的资源,因为JavaScript同源策略的限制,资源无法获取.比如从www.baidu.com 页面去请求 www.google.com 的资源, ...