Mysql Table Foreign Key

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 ...

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 ...

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 ...

Several guidelines on the establishment of the index: 1, a reasonable indexing can speed up the efficiency of data reading, but unreasonable indexing will slow down the database response speed. 2, the more the index, the slower the update data. 3, try to use the index when using MyIsam as an engine (because MySQL uses BTree to store indexes), not InnoDB. But MyISAM does not support Transcation. 4, when your program and database structure / SQL statement has been optimized to the extent that can not be optimized, and the program bottleneck can not be successfully resolved, then ...

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 ...

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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 ...

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 ...

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