Tag: SQL for Beginners

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.

SQL NULL values tutorial: what NULL means, IS NULL and IS NOT NULL, why = NULL fails, how NULL behaves in arithmetic and aggregates, and COALESCE examples.

SQL INSERT INTO tutorial: add one row, several rows at once, insert into specific columns, copy rows with INSERT … SELECT, and common errors.