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二维码的生成细节及原理 - 更多技术 - 清泛网 - 专注C/C++及内核技术
...是分成不同的Block，然后对各个Block进行纠错编码，对于如何分组，我们可以查看QR Code Spec的第33页到44页的Table-13到Table-22的定义表。注意最后两列：
Number of Error Code Correction Blocks ：需要分多少个块。
Error Correction Code Per Blo...
Error installing mysql2: Failed to build gem native extension
I am having some problems when trying to install mysql2 gem for Rails. When I try to install it by running bundle install or gem install mysql2 it gives me the following error:
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MongoDB: Combine data from multiple collections into one..how?
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Doing unions in MongoDB in a 'SQL UNION' fashion is possible using aggregations along with lookups, in a single query. Here is an example I have tested that works with MongoDB 4.0:
// Create employees data for testing the union.
d...
How do I create a user with the same privileges as root in MySQL/MariaDB? [closed]
How do I create a user with the same privileges as root in MySQL/MariaDB?.
1 Answer
1...
Export and Import all MySQL databases at one time
I want to keep a backup of all my MySQL databases. I have more than 100 MySQL databases. I want to export all of them at the same time and again import all of them into my MySQL server at one time. How can I do that?
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What's the difference between INNER JOIN, LEFT JOIN, RIGHT JOIN and FULL JOIN? [duplicate]
...rence between INNER JOIN , LEFT JOIN , RIGHT JOIN and FULL JOIN
in MySQL ?
3 Answers
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How to create a database from shell command?
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cat filename.sql | mysql -u username -p # type mysql password when asked for it
Where filename.sql holds all the sql to create your database. Or...
echo "create database `database-name`" | mysql -u username -p
If you really only want to cr...
MySQL - SELECT WHERE field IN (subquery) - Extremely slow why?
...B and you only select indexed fields (and things are not too complex) than MySQL will resolve your query using only the indexes, speeding things way up.
General solution for 90% of your IN (select queries
Use this code
SELECT * FROM sometable a WHERE EXISTS (
SELECT 1 FROM sometable b
WHERE...
淘宝网采用什么技术架构来实现网站高负载的 - 更多技术 - 清泛网 - 专注C/C...
...淘宝目前的一些底层技术框架以及自己的一些感触来说说如何构建一个可 伸缩，高性能，高可用性的分布式互联网应用。时间过得很快，来淘宝已经两个月了，在这两个月的时间里，自己也感受颇深。下面就结合淘宝目前的一...
XPath OR operator for different nodes
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@user569008: | is the union set operator.
– user357812
Mar 18 '11 at 19:35
1
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