Negation in Queries

You can use negation as a comparison operator or a set operator.

When used as a comparison operator, Amazon SimpleDB returns all items where one of its attribute-value pair does not match the query expression. For example, ['Keyword' != 'Book'] returns items that have a value other than "Book" in the "Keyword" attribute.

This can result in unusual results if the "Keyword" attribute contains multiple values. Because Amazon SimpleDB queries each attribute-value pair individually, this query returns any items that have "Book" and any other value in the "Keyword" attribute.

	Note
	If an item does not have any value within the attribute you are querying, it is not considered and is not included in the result set.

When used as a set operator, Amazon SimpleDB evaluates the predicate expression, resolves it into a set of item names, and finds the complement of the predicate result set by retrieving all item names that do not fall into the predicate result set. For example, not['Keyword' = 'Book'] finds all items that have a "Keyword" attribute with a value equal to "Book" and returns all other items.

This section shows negation queries and their results. To view the source data for the queries, see Sample Query Data Set.

The following table shows some negation queries, how they are interpreted, and the results they return from the sample dataset.