The next type of join that I want to discuss in these posts is a left outer join. We use this mostly, when we know that not all rows are matching.
For example, in the query shown above, I wanted to add up the ordered quantity values for all products. The problem is that if I used an INNER JOIN, I would only get products that match at least one order line.
2025-02-02
It was great to catch up with Joey D’Antoni today and to have him on a SQL Down Under podcast.
Joey D’Antoni is an Architect and SQL Server MVP with over two decades of experience, working in both Fortune 500 and smaller firms. He holds a BS in Computer Information Systems from Louisiana Tech University and an MBA from North Carolina State University. He is a Microsoft Data Platform MVP and VMware vExpert.
2025-02-01
There are two ways you can write common join syntax. There’s an older way to write the query and a new way to write the query.
In the image above, you can see the new way written first, and then the old way written below. The newer syntax was introduced as part of ANSI SQL, back in 1992. It has been recommended for over 30 years now.
When you look at the older syntax, you’ll notice that I’m doing two things in the WHERE clause. I’m both determining how the tables are joined, and I’m also filtering the rows that I want.
2025-02-01
This is a post in the SQL Interview series. These aren’t trick or gotcha questions, they’re just questions designed to scope out a candidate’s knowledge around SQL Server and Azure SQL Database.
Section: Security Level: Medium
Question:
User1 has CONNECT permission to a SQL Server and is a member of the db_datawriter role in the database Database1.
User2 has CONNECT permission to the same SQL Server and is a member of the db_datareader role in the database Database1.
2025-01-31
The most common form of join between two tables is what’s called an inner join.
In the example shown above, I’ve selected some columns from different tables. I’ve got description and product ID from the product table and I’ve got the product group name from the product group. What I wanted was a list of products but I want to know what group they’re part of. So to do that I had to use the products table, but I also had to join to the product groups table so I could get the name of the product group.
2025-01-31
A foreign key is a situation where we store the primary key of one table in another table. It’s very useful. For example, we might need to know which sales transactions were for which customers.
Again, keep in mind that like primary keys, there could be more than one column in a key. While a foreign key can reference a unique key, it’s almost always the primary key.
In the example shown above, the column OrderID is the primary key of the Orders table. It’s highlighted in red. The column CinemaID is the primary key of the Cinemas table, but it has been stored in the Orders table. It’s highlighted in green. We refer to that as a foreign key. Clearly in a system that handles orders for cinemas, we’d need to know which cinema each order is for.
2025-01-30
In the previous post, we saw how CROSS JOIN operations work. Now it’s rare for us to want to have every combination of the rows in each table.
What we usually end up joining on are primary keys and foreign keys. So we should start by defining what primary keys are.
The primary key of a table is a value or combination of values that uniquely identifies a particular row in a table. If we need to refer to a row in a table, and ensure that we’re only talking about one row, it’s how we do that. So how do we identify that one row exactly?
2025-01-29
I recently listened to Your Best Year Ever by Michael Hyatt on Audible.
When the book started with The Best is Yet to Come being announced loudly, I nearly stopped listening. I can’t get the look of Kimberly Guilfoyle screaming that, out of my head.
The way she did that was like an excerpt from a horror movie. She has ruined that phrase for me, for all time.
2025-01-28
The simplest way to join two tables is what’s called a cross-join. So this is where I say from products, cross-join, sales territories.
SELECT *
FROM dbo.Products
CROSS JOIN dbo.SalesTerritories;
Now what that will do though is it will give me every combination of rows from the two tables. So I’ll get one row from the second table for each row in the first table. This is often called a Cartesian product of the two tables and it can quickly end up generating a very large number of rows.
2025-01-28
Most programming languages have some way of forming loops. Now some of them have a variety. For example, a language like Basic or Excel had a For Next loop, a Do While loop, a While Until loop, etc.
In T-SQL, while you could conceivably construct loops manually by using a GOTO statement, no-one does that and it would be considered a bad idea.
Instead, we form all the loops we need by using a WHILE statement. It can be used to create all the variety of loops mentioned above.
2025-01-27