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$nor¶$nor performs a logical NOR operation on an array of one or more query expression and selects the documents that fail all the query expressions in the array. $nor对一个或多个查询表达式的数组执行逻辑NOR操作，并选择数组中所有查询表达式都失败的文档。The $nor has the following syntax:$nor语法如下所示：
$nor Query with Two Expressions$nor查询¶Consider the following query which uses only the 考虑下面的查询，它只使用$nor operator:$nor运算符：
This query will return all documents that:此查询将返回以下所有文档：
price field whose value is not equal to 1.99 and contain the sale field whose value is not equal to true or1.99的price字段，以及值不等于true的sale字段，或者price field whose value is not equal to 1.99 but do not contain the sale field or1.99的price字段，但不包含sale字段，或者price field but contain the sale field whose value is not equal to true orprice字段，但包含其值不等于true的sale字段，或者price field and do not contain the sale fieldprice字段也不包含sale字段$nor and Additional Comparisons$nor和其他比较¶Consider the following query:考虑下面的查询：
This query will select all documents in the 此查询将选择inventory collection where:inventory集合中的所有文档，其中：
price field value does not equal 1.99 andprice字段值不等于1.99，并且qty field value is not less than 20 andqty字段值不小于20，并且sale field value is not equal to truesale字段值不等于trueincluding those documents that do not contain these field(s).包括不包含这些字段的文档。
The exception in returning documents that do not contain the field in the 返回不包含$nor expression is when the $nor operator is used with the $exists operator.$nor表达式中字段的文档时的例外情况是$nor运算符与$exists运算符一起使用。
$nor and $exists¶Compare that with the following query which uses the 将其与以下使用$nor operator with the $exists operator:$nor运算符和$exists运算符的查询进行比较：
This query will return all documents that:此查询将返回以下所有文档：
price field whose value is not equal to 1.99 and contain the sale field whose value is not equal to true1.99的价格字段和值不等于true的sale字段