For beginner
- select specific column use Project Fields
db.inventory.find( { status: "A" }, { item: 1, status: 1, _id: 0 } )
- 1 is mean display
- 0 is mean not display
2. check field exits
db.inventory.find( { b: { $exists: true } } )
3. not equal
db.inventory.find( { qty: { $ne: 20 } } )
4. in array
db.inventory.find( { qty: { $in: [ 5, 15 ] } } )