bài thảo luận ý nghĩa của no sql khái niệm tổng quan NoSQL

1. What is NoSQL ?
 Defination
 Stand for “NOT ONLY SQL”
 Non-relational database
 A flexible database used for big data & real-time web apps
 Multiple types of NoSQL databases
 NoSQL characteristics:
 No Predefined Schemas
 May insert data without creating tables, columns
 Rarely Foreign Keys
 No JOIN operations
 Relationships are not automatically maintained
 Eventual Consistency
 Old copies being replaced by new records
 Inconsistent data until all replacements are complete

 NoSQL vs SQL:
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Example of SQL & NoSQL:


2. Advantages of NoSQL
 Flexible data models
NoSQL databases more relaxed in structure of data:
- Database schema changes do not have to managed as one complicated
change unit
- Application already written to address an amorphous schema
 Economics: clusters of cheap commodity servers to manage the data and
transaction volumes
 Horizontal scaling: most NoSQL databases allow to scale-out horizontally,

meaning we can add cheaper, commodity servers whenever we need to.
 Fast queries: data in NoSQL databases is typically stored in a way that is
optimized for queries. Queries typically do not require joins, so the queries are
very fast.
 Easy for developers: NoSQL require less management, automatic repair and
simple data models
Disadvantages of NoSQL

 NoSQL databases don’t have the reliability functions which
Relational Databases have (basically don’t support ACID).
 This also means that NoSQL databases offer consistency
in performance and scalability.
 In order to support ACID developers will have to implement
their own code, making their systems more complex.
 This may reduce the number of safe applications that
commit transactions, for example bank systems.
 NoSQL is not compatible (at all) with SQL.
 Note: Some NoSQL management systems do use a
Structured Query Language.
 This means that you will need a manual query language,
making things slower and more complex.


 NoSQL are very new compared to Relational Databases, which
means that are far less stable and may have a lot less
functionalities.