How to Use CASE Expressions in SQL
Learn the structure of SQL CASE expressions and use them to classify orders by shipping region, status, and revenue level without changing stored data.
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How to Use SQL Common Table Expressions with WITH
Build readable, multi-stage SQL queries with Common Table Expressions. This tutorial covers CTE syntax, chained aggregations, reusable query stages, common mistakes, and performance considerations.
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SQL Primary Keys, Foreign Keys, and Constraints
Learn how to use SQL keys and constraints to uniquely identify rows, connect related tables, and prevent missing, duplicate, or invalid data.
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SQL Views: Create and Reuse Queries
Learn how SQL views simplify recurring reports by saving reusable queries for customer orders, totals, and filtered results.
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SQL Window Functions: Row Numbers, Rankings, and Running Totals
Use SQL window functions to analyze customer orders while keeping every order row visible. Learn row numbering, rankings with ties, and customer or company-wide running totals.
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SQL Indexes and Query Performance in PostgreSQL
Understand how PostgreSQL indexes help queries find rows efficiently. This tutorial covers single-column and composite indexes, query plans, EXPLAIN ANALYZE, and common indexing mistakes.
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SQL DISTINCT and NULL Values: Finding Unique and Missing Data
Understand how SQL DISTINCT handles duplicate and NULL values, with practical examples using IS NULL, IS NOT NULL, and CASE.
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SQL Transactions: Using COMMIT and ROLLBACK
Learn to group related SQL updates into a single transaction and decide when to permanently save changes with COMMIT or undo them with ROLLBACK.
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SQL CREATE TABLE and ALTER TABLE: A Beginner’s Guide
Learn the fundamentals of SQL table creation and schema changes by building a customer orders table, adding columns, and choosing safe defaults for existing data.
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How to Use INSERT, UPDATE, and DELETE in SQL
Practice changing database table data with SQL INSERT, UPDATE, and DELETE statements, including safe filtering with WHERE and customer record examples.
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