What are the differences between the NoSQL databases and how are they different from traditional relational databases?

Question

There seem to be a lot of new "NoSQL" type databases out there. Some of the popular ones are CouchDB, Cassandra and MongoDB.

What are the differences between such databases and how are they different from tradition relational databases? What are the advantages and disadvantages of picking NoSQL DBs over SQL DBs?

Answer 1

Well,The basic difference are discussed below.Of course,now No-SQL concepts getting popular day by day.But still which one we need to use based on project need or requirements.

1) SQL databases are primarily called as RDBMS. whereas NoSQL database are primarily called as Non-Relational or Distributed database.

2) RDBMS will follow ACID properties i.e Atomcity,Consistency,Isolation,Durability.But in No-Sql it's following CAP (Consistency, Availability and Portioning).

3) In SQL we store data in Tabular formats only.But in No-SQL it uses collection of key-value pair, documents, graph databases or wide-column stores.So No-SQL is Schema free and It can handle structured, semi-structured and unstructured data. But SQL is not Schema free.SQL is having Pre-Defined schema.i.e In SQL if you have table and in that first column is int data type,then you cant store string or Float values.

4) RDBMS follows SQL ( structured query language ) for defining and manipulating the data, which is very powerful. In NoSQL database, queries are focused on collection of documents. Sometimes it is also called as UnQL (Unstructured Query Language). The syntax of using UnQL varies from database to database.Also SQL databases are good fit for the complex query intensive environment whereas NoSQL databases are not good fit for complex queries. On a high-level, NoSQL don’t have standard interfaces to perform complex queries, and the queries themselves in NoSQL are not as powerful as SQL query language.

For Eg..Take Social Eng. sites,We upload photos/videos/Music/Album..etc.For that we get comments, replies to comments,like..etc.Here we can get numbers,special characters..,so almost we cant predict what might be the reply or comments.In this case we go for No-SQL in documented type like below to store the comments.

{
   user_id: ObjectID("65f82bda42e7b8c76f5c1969"),
   update: [
    {
      date: ISODate("2015-09-18T10:02:47.620Z"),
      text: "Nice picture."
},
{
  date: ISODate("2015-09-17T13:14:20.789Z"),
  text: "1234@some smile symbol"
}
{
    date: ISODate("2015-09-17T12:33:02.132Z"),
    text: "...Oh my god.."
  }
 ]
}

In Above if we go for SQL we cant store comments (text above) in column only.We need to store based on type.So we will end up with Big complex query with number of joins with different tables .But SQL is good for Transactions.

5)In most typical situations, SQL databases are Vertically scalable. You can manage increasing load by increasing the CPU, RAM, SSD, etc, on a single server. On the other hand, No-SQL databases are Horizontally scalable. You can just add few more servers easily in your No-SQL database infrastructure to handle the large traffic.

6)SQL databases are best fit for Heavy duty transnational type applications, as it is more stable and promises the atomicity as well as integrity of the data. While you can use NoSQL for transactions purpose, it is still not comparable and stable enough in high load and for complex transactional applications.

7)Examples for No-SQL are MangoDB,Cassandra..etc while for SQL are MySQL,SQL Server etc..

Answer 2

RDBMS is completely structured way of storing data. While the NoSQL is unstructured way of storing the data. And another main difference is that the amount of data stored mainly depends on the Physical memory of the system. While in the NoSQL you don't have any such limits as you can scale the system horizontally.

You'll find that NoSQL database have few common characteristics. They can be roughly divided into a few categories:

key/value stores Bigtable inspired databases (based on the Google Bigtable paper) Dynamo inspired databases distributed databases document databases

Answer 3

Folks, Its a hot debate now a days, SQL or NoSQL, While some admire the elegance in terms of performance of NoSQL databases while others want to live with the legacy of SQL or the RDBMS. While each have its merits and demerits ,I tried to contrast it in brief using some points.

While RDBMS uses relations and joins to make data simpler in database tables     
NoSQL don't use joins for performance.
NoSQL scales freely when we talk in terms of schema and data, while its very tough to scale a RDBMS if data grows.
There are restriction in size of data in RDBMS in terms of data-types capability,  files of any size can be used in NoSQL databases.
Data integrity enforcement comes to play only in RDBMS not in NoSQL databases.
ACID is not the cup of tea for NoSQL databases but for RDBMS.
RDBMS supports complex transactions whereas NoSQL keeps mum for transactions.
NoSQL does not support constraints and validations while its the basic ingredient in RDBMS.
Data is not structured in NoSQL but is highly structured in form of tables in RDBMS.

Its all depends upon the nature and need of the project whether to use SQL or NoSQL.

Answer 4

Agreed, the question is "not which is better," it's "which solution or set of solutions is best for this particular situation."

NoSQL covers a lot of different storage technologies such as CouchDB, MongoDB, Cassandra and Solr.

CouchDB and MongoDB store multi-dimensional data-structures. MongoDB is also schema-less. Cassandra is a column-based storage engine for fast retrieval, and Solr helps solve other problems such as faceting.

NoSQL simply refers to any storage facility which is not interacted with via SQL queries.

Answer 5

They are not better. NOSQL doesn't involve any new innovation or special feature. NOSQL just refers to a collection of software products that are used for certain types of application but don't necessarily have much else in common with each other. NOSQL does not have to mean a non-relational database.

Answer 6

The term NoSQL covers a lot of different approaches to data storage ranging from the simplest key/value storage to sophisticated document databases. It's a catchy buzz word, but not very discriptive IMHO.

For a quick intro you could take a look at the Wikipedia entry for NoSQL