# SQL vs NoSQL databases  --- **What's the difference?** :cold_sweat: * SQL databases are relational (defines relationships in the form of tables.) * noSQL databases are non-relational/distributed (do not require a fixed schema, avoids joins) --- **SQL** databases use structured query language (SQL) for defining and manipulating data & are table-based. SQL requires that you use predefined schemas to determine the structure of your data before you work with it. In addition, all of your data must follow the same structure. :nail_care: --- **noSQL** database, on the other hand, has dynamic schema for unstructured data, and data is stored in many ways: it can be column-oriented, document-oriented, graph-based or organized as a KeyValue store. Does not require a particular query language. :frowning: --- **Examples** **SQL** --> Oracle, Postgres, and MS-SQL **noSQL** --> MongoDB, Redis, Neo4j, Cassandra, Hbase --- ## Examples of the data structure of SQL and NoSQL databases ---  ---  --- ### SQL --- 1. Relational database in tabular format (rows and columns)  --- 2. Online analytical processing, or OLAP uses multidimensional data  --- ### NoSQL --- 1. A column family containing 3 rows. Each row contains its own set of columns.  --- 2. A graph database is essentially a collection of nodes and edges. Each node represents an entity (such as a person or business) and each edge represents a connection or relationship between two nodes. ---  --- 3. Document database  --- 4. Key - Value  --- ## Pros and cons of SQL and NoSQL databases https://www.softwaretestinghelp.com/sql-vs-nosql/ --- | SQL | NoSQL | | -------- | -------- | | -/+ fixed data structure | + flexible data structures | | + normalized data | - redundant data | | + standard and powerful query language | - no standard interface, less powerful queries | --- | SQL | NoSQL | | -------- | -------- | | + commercial and community support due to age of the technology | - less support | | + code free | + hierarchical data | | + data retrieval speed | + handles big data | --- ## Examples of queries for SQL and NoSQL databases :anguished:  --- This question is the source of a number of jokes, including:  --- - The truth is that NoSQL is NOT a standard. It does NOT have a specification. Of any kind. - All it is is a term that describes a whole bunch of completely-different products. --- In reality, you have a number of ways to query NoSQL databases, including: - Ironically, some NoSQL databases now support SQL for querying; - Most NoSQL databases have unique custom interfaces(eg: MongoDB) - Many NoSQL databases support (or have plug-ins to e.g. Hadoop that support) Map/Reduce style "querying". --- ## That being said, here are some examples for queries --- ### Selecting everything from a collection: - SQL ```SELECT * FROM userdetails;``` - NoSQL(MongoDB) ```db.userdetails.find();``` --- ### Selecting with a condition - SQL ```SELECT * FROM userdetails WHERE name = "importantperson"``` - MongoDB ```db.userdetails.find({name:"importantperson"})``` --- ## But switch to anything other than MongoDB and you have new syntax ## (NoSQL is a concept, not a product/language):angry: ---