SQL

SQL aliases explained with six worked examples: rename columns and tables with AS, name calculated columns, shorten joins, filter on an alias with a subquery, and avoid common alias errors.

SQL BETWEEN operator tutorial: filter numbers, dates and text within an inclusive range, use NOT BETWEEN, CASE bands and HAVING, avoid the end-of-day date trap, with seven examples and output.

Learn the SQL IN operator with worked examples: filter by a list of text, numbers or dates, NOT IN, IN with a subquery, IN vs OR, the NOT IN NULL trap, and common errors with fixes.

SQL wildcards explained with worked examples: % and _, SQL Server [ ] sets, NOT LIKE, escaping a literal % or _, database differences, performance and common mistakes.

SQL LIKE operator tutorial: match text patterns with % and _ wildcards, NOT LIKE, case sensitivity by database, and worked examples with output.

SQL COUNT, AVG and SUM tutorial: count rows, total and average a column, COUNT(*) vs COUNT(column), how NULLs are ignored, and examples with output.

SQL MIN and MAX tutorial: syntax, worked examples on numbers, dates and text, WHERE, GROUP BY, HAVING, CASE and window-function variations, NULL rules, common mistakes and a practice exercise.

Learn how SQL LIMIT, TOP and FETCH FIRST restrict the rows a query returns in MySQL, PostgreSQL, SQLite, SQL Server and Oracle, with top-N, pagination and top-N-per-group examples.

Learn the SQL DELETE statement with before-and-after examples: delete by key, by condition, with a subquery or join, inside a transaction, plus DELETE vs TRUNCATE vs DROP.

Learn the SQL UPDATE statement: syntax, five worked examples (single row, several columns, calculations, subqueries and joins), database differences, common mistakes and a safe transaction routine.