CodeProject Archives

What is the difference between a primary and unique key?

Primary and Unique Key

In this article we learn the difference between a primary and unique key, and why both are important to maintaining a relational database structure. All the examples for this lesson are based on Microsoft SQL Server Management Studio and the AdventureWorks2012 database.  You can get started using these free tools using my Guide Getting Started Using SQL […]

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Rank Data with SQL

In this puzzle, we’re going to work through a problem to identify the top and bottom 25 percent to rank student scores. Solving puzzles is a great way to learn SQL.  Nothing beats practicing what you’ve learned. SQL Puzzle Question In today’s puzzle assume you’ve been asked by the head of the Mathematics department to […]

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Learn how to Add, Remove, or Modify values in a SQL Table

Metamorphisis

In this article we’ll discover data modification statements used to modify data in SQL server using the INSERT, UPDATE, DELETE, and MERGE statement. The SELECT, INSERT, UPDATE, DELETE, and MERGE statement are collectively referred to DML (Data Manipulation Language) statements.  These statements allow you to view and modify data.  We extensively cover SELECT in other […]

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Introduction to SQL Server’s Mathematical Functions

Mathematical Functions to Old Way - Slide Rule!

Math Rocks! SQLServer includes many mathematical functions you can use to perform business and engineering calculations.  Many of these aren’t used in typical day-to-day operations; however, there are several commonly used functions we’ll cover. If you not familiar with SQL functions, then I would recommend staring with the Introduction to SQL Server Built-In Functions. All […]

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Foreign and Primary Key Differences (Visually Explained)

Primary and Foreign Keys

In this article we learn the difference between a primary key and a foreign key, and why both are important to maintaining a relational database structure. All the examples for this lesson are based on Microsoft SQL Server Management Studio and the AdventureWorks2012 database.  You can get started using these free tools using my Guide Getting Started […]

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Is it possible to use Joins, Subqueries, and Unions in one Query?

A reader recently asked me to help them solve a problem combining data from multiple tables into a single result.  What was interesting was that the solution used the three ways to combine data that we have recently covered, namely:  JOINS, set operators, and subqueries. Given the comprehensive nature of this problem I thought it […]

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What is the difference between WHERE and HAVING clauses?

In this article learn when to use WHERE and HAVING.  Both perform similar functions, but for different purposes! All the examples for this article are based on Microsoft SQL Server Management Studio and the AdventureWorks2012 database.  You can get started using these free tools using my Guide Getting Started Using SQL Server. How do Where and Having Differ? […]

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How do I combine results from several SQL tables (hint: there are three ways)

Combine data in SQL

Many times in a relational database the information you want to show in your query is in more than one table.  This begs the question “How do you combine results from more than one table?” All the examples for this lesson are based on Microsoft SQL Server Management Studio and the AdventureWorks2012 database.  You can […]

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How to Filter Query Results

In today’s lesson you’re going to learn how to filter query results using the WHERE clause.  This clause is important as only those records matching the where clause’s conditions are returned in the query results. The objectives of today’s lesson are to: Learn about various condition types, such as Equality, Range, and Membership Comprehensive example […]

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2

SQL ACID Explained

What are the  ACID Database Properties? The ACID database properties define the key characteristics SQL databases use to ensure database modification are saved in a consistent, safe, and robust manner. ACID is an acronym to remember the key principles of a transnational system.  ACID stands for Atomic, Consistent, Isolation, and Durability.  Here are some informal definitions: […]

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