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Chapter 12. Advanced Query Concepts > The Propagation of Nulls and Query Result...

The Propagation of Nulls and Query Results

Null values can wreak havoc with your query results because they propagate. Take a look at the query in Figure 12.35. Notice that when parts and labor are added, and either the parts or labor field contains a Null, the result of adding the two fields is Null. In Figure 12.36, the problem is rectified. Notice the expression that adds the two values:

TotalPrice:IIF(IsNull([Parts]),0,[Parts]+IIF(IsNull([Labor]),0,[Labor])


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