[MongoDB]How do I query for fields that have null values?

{column:null}：结果为column的值为null或记录不包含column字段的数据；

{column:{$type:10}}：结果为记录包含column字段且值是null的数据；

{column:{$exists:false}}：结果为记录不包含column字段的数据；

Fields in a document may store null values, as in a notional collection, test, with the following documents:

{ _id: 1, cancelDate: null }
{ _id: 2 }

Different query operators treat null values differently:

• The { cancelDate : null } query matches documents that either contains the cancelDate field whose value is null or that do not contain the cancelDate field:

  db.test.find( { cancelDate: null } )
  

  The query returns both documents:

  { "_id" : 1, "cancelDate" : null }
  { "_id" : 2 }
  

• The { cancelDate : { $type: 10 } } query matches documents that contains the cancelDate field whose value is null only; i.e. the value of the cancelDate field is of BSON Type Null (i.e. 10) :

  db.test.find( { cancelDate : { $type: 10 } } )
  

  The query returns only the document that contains the null value:

  { "_id" : 1, "cancelDate" : null }
  

• The { cancelDate : { $exists: false } } query matches documents that do not contain the cancelDate field:

  db.test.find( { cancelDate : { $exists: false } } )
  

  The query returns only the document that does not contain the cancelDate field:

  { "_id" : 2 }
  

另见

 

The reference documentation for the $type and $exists operators.