Arrays And Lists In SQL Server

Kevin Feasel



Erland Sommarskog has updated his essay on Arrays and Lists in SQL Server.  He’s broken it down into a few parts.  First, the short version:

Now you know why IN (@list) does not work as you hoped for, but if you have a comma-separated list you still need to know to work with it.

The best approach in my opinion is to reconsider having a comma-separated list at all. After all, you are in a relational database, so why not use a table instead? That is, you should pass the data in a table-valued parameter (TVP) instead of that comma-separated list. If you have never used TVPs before, I have an article, Using Table-Valued Parameters in SQL Server and .NET, where I give a tutorial of passing TVPs from .NET to SQL Server, and there is a detailed description exactly of the case of passing a comma-separated list to a TVP. You will find that it is astonishly simple.

Unfortunately, not all environments support TVPs – Entity Framework has no real support for TVPs, reportedly nor has Reporting Services. The same applies if you are on SQL 2005 or earlier, since TVPs were added in SQL 2008. Or you may just be plain stubborn and want to use your comma-separated list. Or you are simply pressed for time, and don’t have the time to learn something new right now.

If you want a longer article on using table-valued parameters, Erland has one of those as well:

This is an article that is intended to get you started with passing table-valued parameters (TVPs) from SQL Server to .NET. I begin with presenting how you use table-valued parameters in SQL Server itself whereupon I give a quick overview of the mechanisms to pass TVPs from ADO .NET to SQL Server.

The main meat of this article are two real-world examples where I use TVPs. The first example is the classical problem of passing a comma-separated list of values to SQL Server, this time through a table-valued parameter. You will be amazed of how simple it is. In the second example I show two ways to load a file with master-detail data into tables in SQL Server. In addition to the examples, there is also some discussion on how you can improve performance when loading large amounts of data.

Despite the appearance of .NET in the title of this article, there is a final chapter that explores the possibilities in other APIs, of which some and some do not support TVPs. This includes Entity Framework which has no for support TVPs. In this chapter I briefly discuss workarounds when TVPs are not available to you.

And for the advanced look at arrays and lists, you have the long-form article:

A problem that has been popular over the years with SQL Server is how to handle a list of values. In the majority of the cases, people have a comma-separated list, because this format is produced by commonly used tools like multi-choice controls in .NET, Reporting Services and other places.

When I say that the problem is popular, I don’t only mean that the questions are commonplace – but so are solutions. You can find no end of blog posts etc that presents string-splitting functions, including performance tests of such functions and there are function that are known to be the fastest etc.

The aim of this article is two-fold: 1) Give a general discussion of how to design string-splitting functions. 2) Present and discuss each method from the angles I bring up in the general discussion. This includes performance, but not only.

Even if you’ve read this article before, it’s worth checking again to refresh your memory and to see his changes.

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