23Sep 2019 by Grant Fritchey 8 Comments

Database Fundamentals #22: Using the Join Operator, CROSS JOIN

Database Fundamentals
While the CROSS JOIN is not used much, and, depending on the size of your data it can be dangerous, there are some uses for it. For example, you may want to write a query that will summarize all the sales for the companies and people in your system. You can do this using what is called an aggregate operation or a GROUP BY: SELECT c.CompanyName, p.LastName, SUM(ft.TransactionAmount) AS 'TransactionTotals' FROM Management.Company AS c JOIN Finance.FinancialTransaction AS ft ON c.CompanyID = ft.CompanyID JOIN Personnel.Person AS p ON p.PersonID = ft.PersonID GROUP BY c.CompanyName, p.LastName; This will add all the values up in the SUM operation for each company and each person that has values so that your data will look like this: The only problem with this is, you can’t…
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15Apr 2019 by Grant Fritchey 2 Comments

Database Fundamentals #21: Using the JOIN Operator, OUTER JOIN

Database Fundamentals, SQL Server
The OUTER JOIN returns one complete set of data and then the matching values from the other set. The syntax is basically the same as INNER JOIN but you have to include whether or not you’re dealing with a RIGHT or a LEFT JOIN. The OUTER word, just like the INNER key word, is not required. OUTER JOIN Imagine a situation where you have a list of people. Some of those people have financial transactions, but some do not. If you want a query that lists all people in the system, including those with financial transactions, the query might look like this: SELECT p.LastName, ft.TransactionAmount, ft.TransactionDate, ft.TransactionTime FROM Personnel.Person AS p LEFT JOIN Finance.FinancialTransaction AS ft ON p.PersonID = ft.PersonID; Except for the addition of the LEFT key word, this…
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03Dec 2018 by Grant Fritchey 9 Comments

Database Fundamentals #20: Using the JOIN Operator, Inner Join

Database Fundamentals
It is entirely possible to try to JOIN two tables on almost any field, as long as the two data types can, in some way, be made to reconcile to each other, you can try to join the tables. But, most database designs assume a much more directly relationship and provide a column or columns in one table that match the identifying column or columns in the other table. INNER JOIN The INNER JOIN will return the parts of both data sets that match. Frequently, what you'll see when joining two tables is the same column name in each table. With that, you have to be sure to identify the owner of each column. I've introduced what is called an alias to make it so I don't have to type…
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08Oct 2018 by Grant Fritchey 3 Comments

Database Fundamentals #19: JOINS

Database Fundamentals
The last Database Fundamentals post introduced the SELECT and FROM commands. We're going to start using JOIN operations shortly, but first, let's explore the idea behind joins. The very concept of relational storage that is the foundation of SQL Server requires you to related one table to another.  You do this through a operation called JOIN. There three basic types of JOINS, INNER, OUTER, and CROSS. Think of them like this. It’s all about relationships. The relationships are only ever between two sets of data. Yes, you can combine lots of tables together through a query, but each JOIN relationship will be between two sets of data. Types of Joins If you take two sets of data and represent them as two circles, they might look like this. An INNER…
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09Jul 2018 by Grant Fritchey 1 Comment

What Is The Preferred Join Operator in SQL Server?

SQL Server, SQL Server 2016, SQL Server 2017, T-SQL
I schedule many of my blog posts at least 2-3 weeks out, so I have time to adjust them, change, them, insert new things into the schedule, what have you. So, as you read this, I'll have written it at least two weeks ago. As I write this, I'm recovering from a very mild, but irritating, cold. I needed to write a blog post, but my stuffed head wasn't coming up with ideas. So, I half-jokingly asked Twitter for any execution plan questions so I could write something. First response, also a joke, was the question at the title of this post: What is the preferred operator when joining tables: Hash Match, Nested Loops or Merge? While my immediate response to this question is, yes. Meaning, they're all preferred, situationally.…
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11May 2015 by Grant Fritchey 13 Comments

Is Performance Better With LEFT JOIN or RIGHT JOIN?

T-SQL
I tend to write my queries using LEFT JOIN. Why? Because logically I see it in my head like this: Give me all the rows from this table and only those rows that match from the other table. But, wouldn't this logic work just as well: Give me only the rows in this table that match the rows from this other table where I'm selecting all of them. I know. If I worked on it some more I could make that a better sentence, but I'm pretty sure the logic is still sound. Only matching rows from one data set, all the rows from another data set. In short, RIGHT JOIN. I read recently that we ought to be making everything into a LEFT JOIN because it performs better. I suspect…
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