SQL Data Types
Last updated: August 26, 2026. A column’s data type defines the values it can store and the operations a database…
Category: Interactive SQL Tutorial
SQL Aggregate Functions: COUNT, SUM, AVG, MIN, and MAX
Last updated: August 27, 2026. Aggregate functions calculate one result from multiple rows. The most common are COUNT, SUM, AVG,…
Practice SQL Queries
Last updated: August 27, 2026. Use the tutorial’s sample tables to practice read-only queries first. Start with a narrow SELECT,…
SQL ALTER TABLE
Last updated: August 27, 2026. Use ALTER TABLE to change an existing table definition. Exact options vary between database systems,…
SQL UNION and UNION ALL
Last updated: August 26, 2026. UNION combines compatible query results and removes duplicate rows. UNION ALL keeps duplicates and usually…
SQL LIKE and NOT LIKE Conditions
Last updated: August 26, 2026. The SQL LIKE condition matches text using wildcard patterns. A percent sign matches zero or…
SQL DISTINCT
Last updated: August 27, 2026. SELECT DISTINCT removes duplicate result rows after the selected expressions have been evaluated. Syntax Example…
SQL SELECT Statement: Retrieve and Filter Data
Last updated: August 27, 2026. The SQL SELECT statement retrieves columns and rows from one or more tables. A clear…
SQL JOINs
Last updated: August 27, 2026. A join combines related rows from two tables. Prefer explicit JOIN … ON syntax because…
SQL Tutorial Sample Database
Last updated: August 27, 2026. The SQL tutorial examples use a small set of related tables. The schema below keeps…