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Given a companies collection where each document has the following structure: { _id: ObjectId("52cdef7c4bab8bd675297efd"), name: 'ZoomInfo', homepage_url: 'http://www.zoominfo.com', blog_url: 'http://zoominfoblogger.wordpress.com/', twitter_username: 'ZoomInfo', founded_year: 2000, email_address: '' } Extract all companies from this collection that have the same Twitter username as the company name. Which query should you use?
Correct Answer: B
db.companies.find( { $expr: { $eq: ['$name', 'twitter_username'] } } ) You have to use $ sign to evaluate twitter_username field. db.companies.find( { $expr: { $eq: ['name', 'twitter_username'] } } ) You have to use $ sign to evaluate name and twitter_username fields. https://docs.mongodb.com/manual/reference/operator/query/expr/