Sql server null a field

So now that we have that covered let's get down to the issue at hand. So based on how tables and columns are setup and how data is stored you may run into an issue where you have data stored in tables that have NULL values and you need to join on these values. Sounds pretty easy, but let's see what happens when this occurs.

First let's create two tables and load some sample data. This is not a very practical example, but it does help illustrate the issue. The first thing we will do is show the data in these two tables. The idea here is that we want to join the tables based on Make, Model and Trim. For most of the records there is some value, but there are a few records where the Trim value is NULL.

The result of the above query matches only three of the four records from the Orders table. So in this example if any value is NULL it will be converted to a space ''. In the results below we can see that we now have more rows, but one of the issues we are facing is that there are also values of space in the table and therefore we are picking up additional joins that we do not want.

The rows that should not be included are highlighted below. This is a value that we know does not exist in our table and therefore will not cause any unwanted joins. It has been a while since this article was first written and there have been a few alternative solutions and suggestions in the comments. We kind of did this in the last query with the , but we didn't actually update the data so we would need to do this each time we ran the query.

Although the ISNULL function is handy, if you are doing large joins having this function in the join clause will slow down the query. A lot of this will also depend on the indexes you have setup and how the indexes are used for the join. In general it is not a good idea to use functions in your joins or on the left side of your WHERE clause, because SQL Server needs to interrogate each value and therefore may negate the use of the index.

Although in some cases there are no other options, so you need to do what you need to do. But be aware of this potential performance issue. As we have seen from the above examples joining NULL values does not work. Another design decision is to not allow NULL values when creating tables and therefore you will not run into these issues. I know this is an old post, but you could also take advantage of SQL Server's underlying set logic Hi Sebastian, yes you could do an update if you are able to change the data.

How to change a table name in SQL Server. Finally, I mentioned stored procedures in this tutorial. Check out the full beginner friendly tutorial here:. I hope you found this tutorial helpful. If you have any questions, leave a comment. Or better yet, send me an email! Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. Skip to content Search for:. The simple things in life are often the best.

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