About RDBMS and non RDBMS [database system]

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 RDBMS( Relational database management system ) It is the mainstream of database management system commonly used in the market , Among them, the most used DBMS Namely Oracle、MySQL and SQL Server.

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Relational database ：

The essence ： The relational database model reduces the complex data structure to a simple binary relationship ( That is, two-dimensional tables ).

Relational database to That's ok (row) and Column (column) In the form of data storage .

Non relational database ：

Concept ： It can be regarded as the function of traditional relational database castration edition , Store data based on key value pairs , No need to go through SQL Layer resolution , Very high performance . meanwhile , By reducing infrequent functions , Further improve performance . at present , Basically, most mainstream non relational databases are free .

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Common non relational databases ：

Common non relational databases include key value databases 、 Document database 、 Search engine and column storage .

for example ： Key database

         Key value database through Key-Value Key value to store data , among Key and Value It can be a simple object , It can also be a complex object .Key As a unique identifier , The advantage is that the search speed is fast , In this respect, it is obviously better than relational database , The disadvantage is that you can't use conditional filtering like a relational database （ such as WHERE）, If you don't know where to find the data , You have to traverse all the keys , This will consume a lot of computation .

The typical usage scenario of a key value database is as Memory cache . Redis Is the most popular key value database .

The evolution of non relational databases ：

because SQL Always dominate DBMS, So many people are thinking about whether there is a database technology that can stay away from SQL, therefore NoSQL The birth of , But with the development, it is found that it is more and more inseparable from SQL. up to now NoSQL In the camp DBMS There will be implementations similar to SQL The function of . Here is “NoSQL” The interpretation of this noun in different periods , From the changes of these definitions, we can see NoSQL The evolution of function ：
1970：NoSQL = We have no SQL
1980：NoSQL = Know SQL
2000：NoSQL = No SQL!
2005：NoSQL = Not only SQL
2013：NoSQL = No, SQL!
NoSQL Yes SQL Made a good supplement , For example, in actual development , There are many business needs , In fact, you don't need a complete relational database function , The function of non relational database is enough . In this case , Use Higher performance 、 A lower cost Of course, a non relational database is a wiser choice . such as ： Log collection 、 Ranking List 、 Timers, etc .