Constraint 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 ...

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 ...

Foreword To technology, I still have awe. Hadoop Overview Hadoop is an open source distributed cloud computing platform based on Map / Reduce model, offline data processing tools. Based on Java development, built on HDFS, first proposed by Google, interested students from the Google troika: GFS, mapreduce, B ...

Dbeaver 1.4.0 This version updates the Oracle plugin and supports OCI driver, program/package, compile/edit, constraint search and other http://www.aliyun.com/zixun/aggregation/18278.html "> Data types. MAC OS x support has been improved. Add a beta version of the Eclipse plug-in. Miscellaneous bug fixes. Dbeaver is a common database management tool and SQL client that supports MySQL,...

NoSQL systems generally advertise a feature that is good performance and then why? relational database has developed for so many years, various optimization work has been done very deep, nosql system is generally absorbing relational database technology, and then, in the end what is the constraints on the performance of relational database? We look at this problem from the perspective of http://www.aliyun.com/zixun/aggregation/9344.html "> System design." 1, index support. Relational data ...