SQL

SQL (Structured Query Language) is the standard query language of relational databases, defining and manipulating data declaratively (DDL/DML/DQL/DCL).

Purpose

To provide a unified, declarative data-manipulation language for relational databases, decoupling applications from storage.

Mechanism

Declarative: describes "what" not "how"; the optimizer generates the execution plan. Sublanguages: DDL (CREATE/ALTER/DROP), DML (INSERT/UPDATE/DELETE), DQL (SELECT), DCL (GRANT/REVOKE). Supports subqueries, JOINs, aggregation, window functions, and CTEs.

Use cases

Relational database query and manipulation
Data analysis and reporting
ETL data transformation
ORM underlying generation

Examples

Input

SELECT name FROM users WHERE age > 18

Output

Names of adult users

Declarative query

Common errors

Concatenating SQL strings causes injection: Use parameterized queries

Related terms

NoSQL is the umbrella term for non-relational databases, including document, key-value, column-family, and graph models, designed for scalability and flexible schemas.

JOIN is the SQL operation combining rows of multiple tables by a join condition; types include inner, left/right/full outer, and cross joins.

An index is an auxiliary data structure (e.g., B+ tree, hash) maintained to speed up queries, trading space for time at the cost of write overhead.

A primary key is the column or column combination that uniquely identifies each row in a table — non-null and unique; the row identity.

A transaction is a group of operations executed as a single logical unit satisfying ACID properties — all or nothing.

Related tools

Beautify or minify SQL queries online. Uppercase keywords, indent clauses, or compress to a single line. Free, private, and 100% client-side.

Pretty-print SQL with keyword uppercasing and clause indentation.

Compress SQL to a single line, removing comments and extra whitespace.

Normalize SQL: uppercase keywords, single spaces, trim.

Compare two SQL statements line by line.

References