Mongodb - Introduction to the use of $exists and the combination of $ne, $nin, $nor, $not in query statements

Come and learn today mongodb Usage of some other query statements in , It mainly contains the following contents :

1、$exists: Query whether a field exists

because mongodb It's a non relational database , therefore , Each record may contain different fields , There may be some fields between different data that have no written values , When you want to filter whether a field exists , You can use $exists To screen .

such as ： Screening user Presence in table age Field records ：

db.getCollection("user").find({age:{$exists:1}})
db.getCollection("user").find({age:{$exists:true}})

Screening user There is no age Field records ：

db.getCollection("user").find({age:{$exists:0}})
db.getCollection("user").find({age:{$exists:false}})

2、 take $exists coordination $ne、$nin、$nor、$not Use

The individual use of each query condition may have been mastered , But when used together , You also need to master . Like you may have learned a lot of skills , But if you don't know how to master these skills , There is still room for improvement .

So let's see take $exists coordination $ne、$nin、$nor、$not Using the demonstration ：

Inquire about user surface name Field equals “ Test Xiaobo ”, also name Records where fields exist ：

db.getCollection("user").find({name:{$ne:" Test Xiaobo ",$exists:true}})

Inquire about user surface age Field not in xxx And age Records where fields exist ：

db.getCollection("user").find({age:{$nin:[18,45,70],$exists:true}})

Inquire about user surface age Greater than or equal to 45 Or is it sex Records with empty fields ：

db.getCollection("user").find({  $nor:[{age:{$lt:45},sex:{$exists:1}}]  })

Inquire about user surface age It's not equal to 45 also age Records where fields exist ：

db.getCollection("user").find({ age:{$not:{$eq:45},$exists:1 }  })

These similar usages above , Sometimes it can help us quickly filter out some abnormal dirty data .

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