##### COMMAND TO SELECT THE DATABASE #####
> use warehouse

##### COMMAND 1 #####
> db.editors.find( { retirement_date: { $exists: true } } ).pretty()

##### COMMAND 2 #####
> db.editors.find( { retirement_date: { $exists: false } } ).pretty()

##### COMMAND 3 #####
> db.editors.find( { zip_code: { $type: "string" } } ).pretty()

##### COMMAND 4 #####
> db.editors.find( { zip_code: { $type: "double" } } ).pretty()

##### COMMAND 5 #####
> db.editors.find( { post_reviews_percentage: { $type : [ "string" , "double" ] } } ).pretty()