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Updating MySQL primary key
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mysql Foreign key constraint is incorrectly formed error
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mysql error texts doesn't help so much, in my case, the column had "not null" constraint, so the "on delete set null" was not allowed
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ZMQ: 基本原理 - 开源 & Github - 清泛网 - 专注C++内核技术
...的一个。 本文的目的是解释ØMQ架构的基本概念，它们是如何组合起来的，以及它们被如此设计的原因。 拓扑 拓扑是ØMQ最主要的概念，除非你知道“拓扑”代表什么，否则将与其他概念混淆更难理解，甚至理解不当。 按...
Insert into a MySQL table or update if exists
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Check out REPLACE
http://dev.mysql.com/doc/refman/5.0/en/replace.html
REPLACE into table (id, name, age) values(1, "A", 19)
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Unioning two tables with different number of columns
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What is the “N+1 selects problem” in ORM (Object-Relational Mapping)?
...cally, a lot of dbms have been quite poor when it comes to handling joins (MySQL being a particularly noteworthy example). So n+1 has, often, been notably faster than a join. And then there are ways to improve on n+1 but still without needing a join, which is what the original problem relates to.
H...
How can I do an UPDATE statement with JOIN in SQL Server?
...Here are some ways to do it in ANSI/ISO (aka should work on any SQL DBMS), MySQL, SQL Server, and Oracle. Be advised that my suggested ANSI/ISO method will typically be much slower than the other two methods, but if you're using a SQL DBMS other than MySQL, SQL Server, or Oracle, then it may be the ...
一文了解大数据领域创业的机会与方向 - 大数据 & AI - 清泛网 - 专注C/C++及内核技术
...据告诉我们，究竟什么是大数据，大数据行业的创业机会如何，未来的创业方向又有哪些。
接触大数据，了解这个行业已经有两年多了，每天都在阅读大量的关于大数据的文献资料和技术文章。如果你要问我什么是大数据？以...
How to change the foreign key referential action? (behavior)
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Example:
I have a UserDetails table refers to Users table:
mysql> SHOW CREATE TABLE UserDetails;
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`User_id` int(11) DEFAULT NULL,
PRIMARY KEY (`Detail_id`),
KEY `FK_User_id` (`User_id`),
CONSTRAINT `FK_User_id` FOREIGN KEY (`User_id`) REFERENCES `Users` (`User_id`)
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:
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mysql - how many columns is too many?
...tables with many rows, modifying the indexes can take a very long time, as MySQL needs to rebuild all of the indexes in the table. Having the indexes split over several table could make that faster.
Depending on your queries and column types, MySQL could be writing temporary tables (used in more co...