Azure-Sql-Db

Another interesting operator is INTERSECT. We saw how EXCEPT takes a set of rows and removes any duplicates, and removes any rows that are also contained in a second set of rows.

INTERSECT is similar in the way it works, but it only returns the rows that are common to both row sets.

You could replace an INTERSECT statement with a WHERE EXISTS clause but if you need to deal with NULLable columns, and as the number of columns increases, you can see that INTERSECT becomes quite an elegant solution.

2025-02-10

Our free SDU Tools for developers and DBAs, now includes a very large number of tools, with procedures, functions, and views. One request that we had some while back, was the ability to format phone numbers using Australian phone number format. To make that easy, we added the FormatAustralianPhoneNumber function.

The only parameter for this function is the phone number that needs to be formatted.

It starts by finding any digits. Then if it finds either 6, 7, 8, or (the standard) 10 digits, it formats the number appropriately.

2025-02-09

We saw how UNION and UNION ALL worked in the last T-SQL 101 post. Sometimes you want to work with two (or more) row sets in other ways.

The EXCEPT clause says that I want all the distinct entries in the first row set unless they also exist in the second row set.

In some database engines, this operator is called MINUS, but EXCEPT is the ANSI SQL standard, and that’s what SQL Server uses.

2025-02-09

Our free SDU Tools for developers and DBAs, now includes a very large number of tools, with procedures, functions, and views. Applications often need to display a list of languages for users to choose from. To make that easy, we have now included a view called Languages.

The Languages view returns details of all the world’s languages, based on ISO 639-1. For each language, the view returns:

• FamilyName
• LanguageName
• NativeLanguageName
• ISO2CharacterCode
• ISO3CharacterCode

The FamilyName indicates the group of languages that the language belongs to. The LanguageName is what we call it in English. The NativeLanguageName is what locals call the language. And then there are the 2 and 3 character codes from the ISO standard.

2025-02-08

There are times when you need to connect together two sets of results into a single result set. The UNION statement is the way we do that.

In the example shown above, I have two SELECT queries. Notice that I could just highlight either one of them, and run them, and I’d see those values. But if I run the whole query, I’ll get back a single set of results that combines data from each of the queries. Note the results:

2025-02-08

Our free SDU Tools for developers and DBAs, now includes a very large number of tools, with procedures, functions, and views. Excel is fascinating in how it stores data. I have friends who joke that everything in Excel is a number or a string, and anything else you see is an illusion.

Date and time values in Excel are odd and use what most call a serial number when they’re stored. It’s common to need to import values from Excel into SQL Server and to export values to Excel.

2025-02-07

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: Development Level: Medium

Question:

While developers don’t mind adding indexes to a database, most people are very nervous about ever removing them.

Tools let us see whether or not an index is being used, but it’s useful to know why the index was added in the first place.

2025-02-07

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: Administration Level: Medium

Question:

You have two tables:

• dbo.Customers
• dbo.Orders

The dbo.Orders table has a column CustomerID that is declared as a foreign key to the CustomerID column in the dbo.Customers table. In the dbo.Customers table, CustomerID is the primary key.

2025-02-06

I’ve made several posts about joins but one option that I haven’t talked about as yet, are what are called non-equi joins.

These are less common, and they often don’t optimize all that well, but it’s worth noting that joins don’t always have to be on equality, or what are called equi-joins.

Non-equi join sounds complex but all we’re saying is that the things that we’re joining on are not equal signs.

2025-02-06

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: Development Level: Medium

Question:

You see the following statement in a query that you are reviewing.

What is the purpose of the NULLIF function in this statement?

SELECT @a / NULLIF(@b, 0);

What was the author trying to achieve?

2025-02-05