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.
Tag: Learn SQL
SQL INSERT INTO Statement: Add New Rows to a Table (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: Sort Query Results ASC and DESC
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, NOT Operators: Combine Multiple Conditions
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: Filter Rows with Conditions (Examples)
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: Remove Duplicate Rows from Results
SQL SELECT DISTINCT returns only unique values. Learn the syntax, DISTINCT on one or several columns, COUNT(DISTINCT), NULL handling and common mistakes.
SQL SELECT Statement: Retrieve Data from a Table (Examples)
SQL SELECT statement tutorial: select all columns or specific columns, use expressions and calculated columns, and see the exact output of each query.
SQL Syntax: Rules, Statement Structure and Clause Order
SQL syntax explained: how statements, clauses and keywords fit together, the clause order rule, case sensitivity, semicolons, quotes, comments and errors.
SQL Quiz: 75 Practice Questions with Instant Answers (Free)
Free SQL quiz with 75 questions on SELECT, WHERE, joins, GROUP BY, subqueries and window functions. 20 random questions per attempt, with instant feedback.
SQL LEFT JOIN: Keep All Rows from the Left Table (Examples)
SQL LEFT JOIN tutorial: return every row from the left table with matching right rows or NULL, find rows with no match, ON vs WHERE filtering, and examples.