Primary Key And Foreign Key In Mysql

If a computer manufacturer, its database holds machine and accessories product information. The table used to save the whole product information is called pc; the table used to save the parts supply information is called parts. There is a field in the pc table, used to describe the type of CPU used in this computer; there is a field in the parts table, the description of the CPU model, we can think of it as a list of all CPU models. Obviously, the CPU used by this manufacturer must be a model that exists in the supply information sheet. At this time, two tables ...

Foreign key role: Maintain data consistency, integrity, the main purpose is to control the data stored in the foreign key table. So that the two forms related, the foreign key can only refer to the value of the column in the surface! For example: ab two tables a table has the customer number, customer name b table stored in each customer's order After the foreign key You can only delete clients in Table a if you do not have Customer x in the b table. Prerequisites: The columns in this table must be the same as the foreign keys (the foreign key must be a foreign key). Specify ...

Usually speaking of foreign keys, we only mention "the purpose of the foreign key is to determine the referential integrity of the data." However, what foreign keys specifically include the actions and meanings? 1, set the outer chain: (1), create a foreign key through create table: see 2 lines of code is built in the table command: create table city (... key idx_fk_country_id (country_id), constrain ...

In MySQL, using the id field of the auto_increment type as the primary key of a table and using it as a foreign key to other tables to form a "master-slave table structure" is a common usage in database design. However, in the specific generation of id, our order of operations is generally: insert records in the main table, and then get the automatically generated id, based on it to insert the record from the table. There is a difficulty here, is inserted into the main table record, how to get it corresponds to the id. The usual practice is through "select max (id) from table ...

What is a column-oriented open source distributed database HBase release time: 2012.04.16 14:41 Source: News and Author: HBase is a distributed, column-oriented open source database, developed by the Apache Foundation. Unlike a generic relational database, HBase is a database suitable for unstructured data storage. It is based on a column rather than a row based pattern. User stores data ...

With the rise of internet web2.0 websites, the relational database has become a very hot new field, the development of the non relational database products is very rapid. 　　But the traditional relational database in dealing with web2.0 website, especially the super large-scale and high concurrent SNS type web2.0 pure dynamic website already appeared to be powerless, has exposed many insurmountable problems, for example: 1, high configured--to the database higher concurrent reads and writes the demand WEB2.0 website to be based on user personalized information to generate real-time dynamic ...

Intermediary transaction http://www.aliyun.com/zixun/aggregation/6858.html ">seo diagnose Taobao guest cloud host technology Hall in recent years, with the development of the Internet and the popularization of network marketing, the establishment of personal websites, Promotion of network Marketing has been deep into people's lives and work, personal construction station has gradually become popular throughout the IT industry. Personal site by virtue of its construction at random, the management of freedom and other characteristics and quickly by many webmaster favorite. But after the construction of the website idea ...

Intermediary transaction SEO diagnosis Taobao guest Cloud host technology lobby A5 source code to do a good job source code download, focus on serving the Chinese webmaster, for a large number of source enthusiasts to provide convenience. 　　February mainly for community forums, blog microblogging, Enterprise construction Station, CMS, shop Mall and other categories for you to clean up the source code update dynamic; What's the following to see what good source code has been updated, what new features have been added, what functions have been optimized, what bugs are fixed ... Community Forum Source Thinksaas is a lightweight open source ...

There are a few things to explain about prismatic first. Their entrepreneurial team is small, consisting of just 4 computer scientists, three of them young Stanford and Dr. Berkeley. They are using wisdom to solve the problem of information overload, but these PhDs also act as programmers: developing Web sites, iOS programs, large data, and background programs for machine learning needs. The bright spot of the prismatic system architecture is to solve the problem of social media streaming in real time with machine learning. Because of the trade secret reason, he did not disclose their machine ...

The intermediary transaction SEO diagnoses Taobao guest Cloud host Technology Hall Successful website has the reference place, for the novice that involves the Internet to start a business, how to make the first bucket gold quickly through the construction station, understands and borrows the profit pattern of the successful website is very necessary. One, you can also be successful webmaster two, share the shares of the city network above details can be to the article "Internet Entrepreneurship Success (10): You can also be a successful webmaster" in Reading three, car China to do the most practical car website: Automotive China Network (www.