Common Questions Archives

Here is a list of common questions I’ve been asked by my students in class or via email.

Whether you’re looking to find out the difference between of primary an foreign key or want to know what is a data dictionary, you’ll find answers to many common problems.

 

If you have a question that I haven’t answered, please ask!  You can contact me here.  I’m always looking to see what you guys need helps with, as it helps me learn!  I love helping!

All the examples for this lesson are based on Microsoft SQL Server Management Studio and the sample databases AdventureWorks and WideWorldImporters.  You can get started using these free tools using my guide Getting Started Using SQL Server

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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23

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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5

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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13

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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20

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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1

What are the Top Ten Databases?

Everyone has their favorite DBMS, is your favorite one of the top databases? Though some non-relational products have entered the top ten, the relational paradigm remains firmly entrenched in the database world.  However specialized database types such document store databases and wide column stores are gaining in popularity to become top databases. Top of the […]

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2

SQL ACID Explained

What are the  ACID Database Properties? The ACID database properties define SQL database key properties to ensure consistent, safe and robust database modification when saved. ACID is an acronym that helps to remember the fundamental principles of a transnational system. ACID stands for Atomic, Consistent, Isolation, and Durability.  Here are some informal definitions: Atomic – In a transaction […]

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