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: SQL
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…
Fix ‘Cannot Load from mysql.proc’ in MySQL
Last updated: August 25, 2026. The mysql.proc error normally means the server binaries and MySQL system tables belong to different…
How to Back Up and Restore a MySQL Database
Last updated: August 25, 2026. A logical MySQL backup is a portable SQL file containing the statements needed to recreate…
SQL Reference and Interactive Tutorial
Last updated: August 27, 2026. SQL retrieves and changes data in relational databases. Begin with SELECT, filtering, and sorting, then…
Determine the MySQL Version from the Command Line
Last updated: August 27, 2026. Use the client version command to identify the installed command-line program, and query the server…
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…