Tag: SQL for Beginners

SQL IN operator tutorial: match a column against a list of values, NOT IN, IN with a subquery, IN vs OR, the NULL trap with NOT IN, and examples with output.

SQL wildcards explained: the % and _ characters, SQL Server [ ] ranges, escaping literal % or _, worked examples with results 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: find the lowest and highest values in a column, use them with WHERE and GROUP BY, get the full row with a subquery, plus NULL rules.

SQL TOP, LIMIT and FETCH FIRST limit the rows a query returns. Syntax for MySQL, SQL Server, PostgreSQL and SQLite, OFFSET pagination and top-N examples.

SQL DELETE tutorial: remove rows with WHERE, delete using a subquery or join, DELETE vs TRUNCATE vs DROP, and how to avoid deleting everything.

SQL UPDATE tutorial: change one or many columns with SET and WHERE, update using calculations, update from another table with a join, and stay safe.

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.