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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.

SQL ORDER BY clause tutorial: sort results ascending or descending, sort by several columns, by expressions and aliases, handle NULLs, and see each result.

SQL AND, OR and NOT operators let you combine several WHERE conditions. Learn precedence, parentheses, worked examples with results and the mistakes to avoid.

SQL WHERE clause tutorial: filter rows with =, <>, >, <, BETWEEN, LIKE and IN, quote text correctly, use WHERE in UPDATE and DELETE, plus common mistakes.

SQL SELECT DISTINCT returns only unique values. Learn the syntax, DISTINCT on one or several columns, COUNT(DISTINCT), NULL handling, DISTINCT vs GROUP BY and common mistakes, with worked examples.

Learn the SQL SELECT statement: select specific or all columns, add calculated and text columns, preview WHERE and ORDER BY, and fix the most common SELECT errors, with exact output for every query.

SQL syntax explained: how statements, clauses and keywords fit together, the clause order rule, case sensitivity, semicolons, quotes, comments and errors.