Your Ultimate Guide to SQL Join: INNER JOIN – Part 1

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Inner join, outer join, cross join? What gives?

It’s a valid question. I once saw a Visual Basic code with T-SQL codes embedded in it. The VB code retrieves table records with multiple SELECT statements, one SELECT * per table. Then, it combines multiple result sets into a record set. Absurd?

To the young developers who did it, it was not. But when they asked me to evaluate why the system was slow, that issue was the first to catch my attention. That’s right. They never heard of SQL joins. In fairness to them, they were honest and open to suggestions.

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SQL Server Inner Join Basics with Examples

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Introduction

T-SQL allows us to combine records from more than one table and return them as a single result set. This is achieved through the concept of joins in SQL Server.

This opportunity is often necessary because data in relational databases are typically normalized. For example, we have employee data spread across two or more tables. The first table would be the basic customer data and called employee. The second table would be the department.

The data consistency requires the correct relationship between the customer and the department. Returning the complete data for a set of employees and their departments requires to join both tables.

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