Published on

December 14, 2007

Understanding NULL Settings in SQL Server Integration Services (SSIS)

When working with SQL Server Integration Services (SSIS), it’s important to understand the various NULL settings and their implications. Failure to do so can lead to unexpected results and data inconsistencies. In this article, we will explore the different NULL settings in SSIS and how they affect data import and destination.

Scenario

Let’s consider a common scenario where we need to import data from a text file into a SQL Server database. The text file contains three columns: MyDate, MyInt, and MyText. We have a data flow task with a flat-file source connected to an OLEDB destination.

Now, what happens when we encounter a blank value in the text file? By default, SSIS treats a blank value as a specific default value. For example, a blank date will be converted to “1st Jan 1753”, an integer will become “0”, and text will become an empty string (“”). This default behavior may not always be desirable, especially if “0” is a legitimate value in the text file.

Handling NULL Values

To handle NULL values from the flat file, we can use a simple checkbox on the flat file source component. By checking the “Retain null values from the source as null values in the data flow” option, we ensure that NULL values from the flat file are preserved as NULL values in the resulting OLEDB destination.

With this setting enabled, the imported dataset will accurately reflect the NULL values from the source file.

Keep NULLs Option

There is another important setting to consider when dealing with NULL values in SSIS – the “Keep NULLs” option on the OLEDB destination component. This setting controls what happens when there are default constraints on the destination table.

If the destination table has default constraints on each column, such as a default date of today or a default number of -1, we need to decide whether we want these default values to be overwritten by NULL values from the source file or to simply apply their specified defaults.

By default, the “Keep NULLs” option is unchecked, which means that the default values on the destination table will be overwritten by NULL values from the source file. If the option is checked, the default values will be retained and applied instead of the NULL values.

Conclusion

Understanding the NULL settings in SQL Server Integration Services is crucial for ensuring accurate data import and consistency. By properly configuring the NULL settings, we can handle NULL values from the source file and control the behavior of default values on the destination table.

Remember to check the “Retain null values from the source as null values in the data flow” option on the flat file source to preserve NULL values. Additionally, consider the “Keep NULLs” option on the OLEDB destination to determine how default values should be handled.

By mastering these concepts, you can avoid confusion and ensure the integrity of your data when working with SSIS.

Thank you for reading!

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