Sql-Server

There are times that you need to be able to query the database and its internal structures rather than querying the user tables.

In the example above, I’ve asked for details of all the databases, and then for details of all the schemas in the current database, followed by details for all the tables and columns in the current database.

These are a well-designed set of system views that are easy to work with. They are often referred to as catalog views. You can even see all of them as part of querying sys.views.

2025-03-10

Our free SDU Tools for developers and DBAs, now includes a very large number of tools, with procedures, functions, and views. I do a lot of reviewing of database designs and one thing I always check for is the use of user-defined data types. I’ve had situations where these have caused me substantial issues. So we added a tool that can help to find these. It’s called ListUserDefinedDataTypes.

The procedure takes one parameter.

2025-03-09

It’s also possible to create the command dynamically before you execute it.

In the example above, I’ve set a number of different parts of a SQL statement into variables, and then used them to construct a complete SQL statement that I’ve then executed. I just have to create a valid SQL statement as a string.

Warning

While this might seem really, really convenient, and it can be incredibly useful, it is something you need to be extraordinarily careful with. One of the problems with this is that it can easily open you up to what’s called SQL injection attacks.

2025-03-08

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 are writing a script to change the code in a T-SQL function.

You can choose to either DROP IF EXISTS and CREATE the procedure, or to use an ALTER statement.

What advantage would you get from using an ALTER statement?

2025-03-07

In T-SQL, the way we execute a stored procedure is to use the EXECUTE statement. We can write it as EXECUTE or as EXEC. You’ll almost always see it written as EXEC.

In the first example above, I’ve executed a stored procedure called dbo.GetCinemaChanges. Note that I’ve included the dbo schema in the name of the procedure. For procedures like this, you should always include the schema name.

The procedure also takes one parameter called @CurrentDate and set it to the 28th February 2012.

2025-03-06

In a previous post, I described the issues with measuring quantities in warehousing systems. I showed how you could well need to measure more than just quantities purchased or sold. You often need to deal with the hierarchies of containers that goods are supplied in.

But while food wholesale systems will need to deal with quantities like I described in that post, they often have another layer of complexity. Items are often sold by:

2025-03-05

Stored procedures are prepackaged groups of T-SQL statements. They can also be written in other languages, but most of the time they’ll be written in T-SQL.

There are pros and cons with using stored procedures.

In the example shown, I use the EXEC statement to execute a stored procedure called SDU_Tools.ListAllDataTypesInUse.

Parameters

The procedure also takes a number of parameters. By using different parameters values, I can change the behaviour of the stored procedure.

2025-03-04

I mentioned earlier that CTEs can be used to clean up or tidy more complicated queries. You will find people though, who really don’t like them at all. My aim here isn’t to argue for or against them, as it’s a complex topic, but to make sure you know how to write queries with them, and more importantly, to be able to read queries that use them. At this point, I want you to understand the syntax.

2025-03-02

After one of my recent posts, I was asked what an outer quantity was. This term is common in warehousing and logistics. So many business applications assume that you sell things by quantity, and that you just count the number in vs the number out.

But that’s not how it works.

A system that’s useful for these tasks, understands way more than that. The terms unit, inner, outer, shipper, layer, and pallet refer to different levels or units of packaging and organization in the supply chain. Here’s a breakdown of each term:

2025-03-01

One of the challenges with subqueries is they can get very, very messy if you need to use them more than once. So for example, in the first query above, I’ve created a derived table called BulkProducts. But what if I needed to derive that same table again? Then I would end up with yet another copy of all that code. (And obviously it might be far more complex)

A more common problem is that in a SELECT statement, I might be selecting subqueries but every single time I might be needing to calculate a sub-query to get the values.

2025-02-28