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Chapter 11. Advanced Query Techniques > The Propagation of Nulls and Query Resu...

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 11.35. Notice that when parts and labor are added, and either the Parts field or the Labor field contains a Null, the result of adding the two fields is Null. In Figure 11.36, the problem is rectified. Figure 11.37 shows the design of the query that eliminates the propagation of the Nulls. Notice the expression that adds the two values:

TotalPrice: Nz([Parts]) + Nz([Labor])


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