SQL 201 Tag Archives

1

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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22

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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18

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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6

SQL Inner Join to Two or More Tables

Use an SQL INNER JOIN when you need to match rows from two tables.  Rows that match remain in the result, those that don’t are rejected. The match condition is commonly called the join condition.  When the match conditions involve equality, that is matching exactly the contents of one column to another, the sql inner […]

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