What is SQL?
SQL is the language you use to ask a relational database questions and to add, change or delete its data.
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SQL (Structured Query Language) is the standard way to talk to relational databases. Instead of telling the computer how to find things, you describe what you want: give me the names of customers from Paris sorted by last order. It reads almost like English, which is why it has survived since the 1970s with only small changes.
The four verbs you use most are SELECT to read, INSERT to add, UPDATE to change and DELETE to remove. WHERE filters rows, JOIN combines tables, GROUP BY summarises. PostgreSQL, MySQL, SQLite, Oracle and SQL Server all speak SQL with small dialect differences. Analysts, backend developers and administrators all write it daily.
SELECT name, city
FROM customers
WHERE city = 'Paris'
ORDER BY name;See also: What is a database? and What is an index (database)?
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See also
- 0067 Your first SQL queries: SELECT, WHERE, ORDER BY, LIMIT and GROUP BY Read data from a table, keep only the rows you want, sort them, take the first few, and summarize groups with COUNT,… Beginner · Step by step · Any system Article Queries 15 Oct 2026
- 0069 NULL in SQL: why = NULL never matches and how to handle missing values NULL means "unknown", so comparisons with it are neither true nor false. Use IS NULL, COALESCE and careful aggregates to avoid rows… Intermediate · Explains an idea · Any system Article Queries 15 Oct 2026
- 0071 Fix: column “x” must appear in the GROUP BY clause or be used in an aggregate function PostgreSQL rejects a grouped query that selects a column with more than one possible value per group. Add the column to GROUP… Intermediate · Fixes an error · Any system Article Queries 15 Oct 2026
- 0077 SQL cheat sheet: a runnable reference for everyday queries One SQL file that builds a tiny database and demonstrates filtering, sorting, grouping, joins, CASE, CTEs, window functions, safe updates and indexes.… Beginner · Cheat sheet · Any system Script Joins · Queries 15 Oct 2026
- 0215 mysql command-line client cheat sheet The connection options, built-in commands and everyday SQL you need in the mysql (and mariadb) command-line client, on one page. Beginner · Cheat sheet · Any system Article Administration · Queries 15 Oct 2026
- 0260 Design and build a library database in SQLite: tables, keys, joins, reports and backups Model books, members and loans, create tables with keys and constraints, load sample data, write join and aggregate reports, add indexes checked… Beginner · Guided project · Any system Article Joins · Queries 15 Oct 2026
Repos in the wild
- DuckDB duckdb/duckdb An in-process analytical SQL database. Run fast SQL directly on CSV, Parquet and JSON files, from the command line or inside Python and other languages. GitHub
- SQLite (official Git mirror) sqlite/sqlite The source tree of SQLite, the self-contained SQL database engine embedded in phones, browsers and countless applications, mirrored to GitHub by its developers. GitHub
History
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