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27 votes

How mongoDB projection affects performance?

By default, queries return all fields in matching documents. If you need all the fields, returning full documents is going to be more efficient than having the server manipulate the result set with ...
Stennie's user avatar
  • 10.3k
3 votes

How to represent NULL in relational algebra?

There are no NULL values in relational algebra. Here you can use the antijoin operator ▷: πROLLNO, NAME(STUDENT ▷ENROLLMENT) that selects all records from STUDENT where the ROLLNO is ...
miracle173's user avatar
  • 7,692
2 votes

How mongoDB projection affects performance?

With a projection, you can achieve a situation where the result set comes directly from the index. If you have compound index {x:1, y:1, z:1} where none of x,y,z is _id, you need to project {_id:0, ...
JJussi's user avatar
  • 5,703

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