As a database is the backbone of any application, choosing between a SQL-based (relational) or NoSQL-based (non-relational) database for a project is one of the most crucial decisions to make. Both are popular database types, offering unique characteristics and having their own pros and cons.
Difference Between SQL and NoSQL
This article will assist you in understanding the key differences between SQL and NoSQL databases. Before that, let us briefly understand what exactly SQL and NoSQL databases are and what their pros and cons are.
What is SQL Database?
SQL databases support Structured Query Language (SQL), a domain-specific language for accessing and manipulating data stored in relational databases. It is especially used to handle structured data, i.e., data having relations among variables and entities. Relational databases store data in the form of tables, also known as relations, i.e., rows and columns. They depend on the relational model proposed by E.F. Codd in 1970.
In relational databases, rows are referred to as tuples or records, and columns as attributes. Each table or relation represents one entity type, tuples or records are instances of that entity type, and columns attribute values to each instance. Though SQL is not the only language to access or manipulate data in relational databases, it is the most popular one, and many databases offer the option of using SQL.
Some of the popular examples of SQL databases are Oracle, Microsoft SQL Server, Sybase, PostgreSQL, Ingres, and Microsoft Access. SQL databases follow the ACID properties. ACID stands for Atomicity, Consistency, Isolation, and Durability. Let us discuss each of these properties in brief.
- Atomicity: Every transaction is a single atomic unit. This property ensures that every transaction either takes place entirely or fails completely. There is no scope for a partially completed transaction.
- Consistency: It ensures that a database is in a consistent state before and after processing any transaction.
- Isolation: Multiple transactions might happen at the same time, and the isolation attribute ensures that each one happens on its own without causing a database to become inconsistent.
- Durability: It ensures that updates and modifications to a database after a transaction are executed, stored, and written to disk. They should last even if the system fails.
Benefits of SQL
Following are the advantages of SQL:
- Flexible and well-established.
- SQL statements are easy to learn and understand.
- A single SQL query can handle a large number of transactions.
- SQL supports indexes that ensure the fast searching and querying of data.
- Foreign keys in SQL databases support faster retrieval of data from multiple tables.
- ACID properties ensure that data in a database is consistent.
Limitations of SQL
Below are some of the limitations of SQL:
- SQL databases can only store structured data and not unstructured data.
- The more the number of tables, the lower is the response given to user queries.
- SQL databases require a large amount of physical memory.
- A large amount of data in a database makes the system complicated.
What is NoSQL Database?
NoSQL databases are those that store data differently than SQL databases, i.e., in a non-tabular format. Unlike SQL databases, these databases can have unstructured data. NoSQL stands for "not only SQL". Such databases have wide applications in real-time web applications and big data. Four different types of NoSQL databases based on their data models are:
- Document databases: It stores data in documents analogous to JavaSCript Object Notation (JSON) objects. Data in documents is stored in the form of fields and values. Values can be of different types, like strings, objects, booleans, numbers, or arrays.
- Key-value databases: It stores each data item in the form of a key-value pair.
- Wide-column store: This type of NoSQL database stores data in tables, rows, and dynamic columns.
- Graph databases: It uses a graph-like structure to store data. Nodes in a graph store data, like people, things, or places. Edges represent information about the relationships between data.
NoSQL databases are schemaless databases, i.e., they do not have a fixed schema like relational databases. Popular examples of NoSQL databases include Apache Cassandra, MongoDB, Amazon DynamoDB, Bigtable, CouchBase, and CloudDB. As relational databases follow ACID properties, NoSQL databases follow the CAP theorem. CAP stands for Consistency, Availability, and Partition Tolerance. Let us briefly see what each of these means.
- Consistency: It ensures that all nodes in a network see the same data at the same time.
- Availability: It guarantees that every request receives a response, whether it is a success or failure.
- Partition tolerance: It ensures that the system keeps running even if some messages in a network are dropped or lost.
Benefits of NoSQL
Following are the benefits of NoSQL databases:
- NoSQL databases use sharding, meaning that data is split into small chunks and stored on multiple machines, preserving the order of data. Hence, these databases ensure high scalability.
- There is an auto replication feature in NoSQL databases that ensures the high availability of data.
Limitations of NoSQL
Some of the significant limitations of NoSQL are:
- Its major focus is on providing storage for large data sets, and apart from that, it does not offer much functionality as compared to relational databases.
- Data management is more complex than relational databases.
- Only a few NoSQL databases guarantee atomicity and data integrity.
NoSQL vs SQL: A Head-to-Head Comparison
Here are some key differences between SQL and NoSQL databases.
| Parameters | SQL | NoSQL |
| Definition | SQL databases are called relational databases that are based on the relational model and mostly use SQL to retrieve and manipulate data. | NoSQL databases are called non-relational databases and store data in a format other than relational databases. |
| Query language | These databases use Structured Query Language (SQL). | There is no declarative query language for NoSQL databases. |
| Schema | They have a predefined schema. | They are schema-less databases. |
| Scaling | SQL databases are vertically scalable. | NoSQL databases are horizontally scalable. |
| Hierarchical data storage | They are not suitable for hierarchical data storage. | They are ideal for hierarchical data storage. |
| Open-source | There are open-source SQL databases, like PostgreSQL and MySQL. Also, the commercial SQL database is Oracle Database. | NoSQL databases are open-source. |
| Ideal for | They are best suited for multi-row transactions. | They are ideal for unstructured data, like documents or JSON. |
| ACID vs CAP | SQL databases follow ACID properties. | NoSQL databases follow the CAP theorem. |
Conclusion
Choosing a database is an important factor to consider when planning a project. Before deciding on SQL vs NoSQL databases, consider your project's data requirements and make your selection accordingly. Both of these databases have distinct features and their own set of advantages and disadvantages. If your project requires unstructured data, a NoSQL database is the obvious choice. SQL databases are ideal for complex transactions because they ensure data integrity and atomicity.
This article should have helped you understand the key differences between SQL vs NoSQL databases.
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