|Appendix A: Missing values ||
N/A values are handled automatically in selection and value expressions and tabulations.
Assuming that missing values are represented by our special N/A values, what happens when these values are used in a computation? Specifically, if we create a computed column that references one or more other columns, and those columns contain N/As, what will be the value of the computed column?
For example, if col3 is col1+col2 and one or both of col1 and col2 are N/A, what will col3 be? What if col3 is col1>col2 or round(col1;10)?
For most functions and operators, if any argument is N/A, the result is N/A, but this is not always true. See the description of each operator and function for details about N/A handling.
What happens when N/A values are encountered in a quick summary or tabulation?
For example, when summing the values in a particular group of rows, what if some of the values are N/A?
The answer is that, as a general rule of thumb, N/A values are ignored. In the case of sum, for example, the result is the sum of the non-N/A values. But there are exceptions to the rule. See the description of each summary type for details about N/A handling in quick summaries, tabulations, and cross tabulations.