SQL
SQL (Structured Query Language) is the standardized query language for relational databases. With SQL you can query, insert, update, delete data and manage database structures.
Databases are the foundation of almost every piece of software – and SQL is the language you use to talk to them. For over 40 years SQL has been the standard for relational databases and is supported by virtually all major database systems. From simple queries to complex reporting and managing huge datasets – SQL is essential for developers, analysts and admins. Despite the rise of NoSQL, SQL remains the most widely used database language in the world.
What is SQL?
SQL is a declarative language designed for managing and querying data in relational database management systems (RDBMS). It includes DQL (Data Query Language) for SELECT, DML (Data Manipulation Language) for INSERT, UPDATE, DELETE, DDL (Data Definition Language) for CREATE, ALTER, DROP of tables, and DCL (Data Control Language) for GRANT and REVOKE. Relational databases store data in tables with rows and columns and use relations between tables via primary and foreign keys. The SQL standard is maintained by ISO/IEC; each system (MySQL, PostgreSQL, SQL Server, Oracle) adds its own extensions.
How does SQL work?
SQL commands are sent as text to the database management system (DBMS). The query parser checks syntax, the query optimizer produces an execution plan, and the storage engine runs the operations. For SELECT the database scans the relevant tables, applies WHERE, ORDER BY and GROUP BY and returns the result. Indexes greatly speed up access to frequently queried columns. Transactions (BEGIN, COMMIT, ROLLBACK) ensure related operations either all succeed or none do (ACID).
Practical Examples
An online shop uses SQL to filter products by category, price and availability and show matching results to the customer.
A reporting system uses complex SQL joins and aggregates to generate monthly sales reports across multiple tables.
A CRM uses SQL to manage customer data, contact history and sales pipelines in a relational database.
A data warehouse uses SQL for ETL processes that combine, transform and load data from source systems for analysis.
A web app uses parameterized SQL to read and write user data safely and efficiently to a PostgreSQL database.
Typical Use Cases
Backend development: Almost every web app uses SQL for persistence in relational databases
Business intelligence: Analysts use SQL for complex reports and ad-hoc queries on large data
Data migration: SQL scripts transform and move data between systems and database formats
Administration: DBAs use SQL for user management, permissions, backups and performance tuning
Data engineering: ETL pipelines use SQL to load and prepare data from multiple sources into data warehouses
Advantages and Disadvantages
Advantages
- Universal standard: SQL is supported by all major relational databases (MySQL, PostgreSQL, SQL Server, Oracle)
- Declarative syntax: You describe the desired result, not the steps – SQL stays readable
- Power: From simple queries to complex analytics in one language
- Data integrity: Relational databases with SQL enforce consistent data (ACID) via constraints and transactions
- Large ecosystem: Tools, ORMs, documentation and community make getting started and daily work easier
Disadvantages
- Vertical scaling: Relational databases scale mainly vertically (bigger hardware), which has limits at very large scale
- Rigid schemas: Table structures must be defined upfront; changes need migrations that can be complex
- Join complexity: Queries across many related tables can become hard to read and slow
- Not ideal for unstructured data: Documents, graphs or time series fit better in specialized NoSQL systems
Frequently Asked Questions about SQL
What is the difference between SQL and NoSQL?
Which SQL database should I choose?
What is SQL injection and how do I protect against it?
Related Terms
Want to use SQL in your project?
We are happy to advise you on SQL and find the optimal solution for your requirements. Benefit from our experience across over 200 projects.