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Nulls and Query Results

Null values in your table's fields can noticeably affect query results. A Null value is different from a zero or a zero-length string, which indicates that the data doesn't exist for a particular field; a field contains a Null value when no value has yet been stored in the field. (As discussed in Chapter 2, you enter a zero-length string in a field by typing two quotation marks.)

Null values can affect the results of multitable queries, queries including aggregate functions (Totals queries), and queries with calculations. By default, when you build a multitable query, only records that have non-Null values on the “many” side of the relationship appear in the query result (discussed earlier in this chapter, in the “Pitfalls of Multitable Queries” section).


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