1.查询所有数据

db.inventory.find()
相当于SQL
SELECT * FROM collection

> db.logs.find();
{ "_id" : ObjectId("5cd0983de8271827134eeb37"), "date" : "2019-06-19", "content" : "crash" }
{ "_id" : ObjectId("5cd0c9a4c33b2d6f4c83018d"), "date" : "2019-06-25", "content" : "warning" }
> 

2.等于条件查询

db.inventory.find( { status: "D" } )
相当于SQL
SELECT * FROM inventory WHERE status = "D"

> db.logs.find({'date':'2019-06-25'});
{ "_id" : ObjectId("5cd0c9a4c33b2d6f4c83018d"), "date" : "2019-06-25", "content" : "warning" }
> 

3.AND条件查询

db.inventory.find( { status: "A", qty: { $lt: 30 } } )
相当于SQL
SELECT * FROM inventory WHERE status = "A" AND qty < 30

> db.logs.find({'date':'2019-06-25','content':'warning'});
{ "_id" : ObjectId("5cd0c9a4c33b2d6f4c83018d"), "date" : "2019-06-25", "content" : "warning" }
>

4.OR条件查询

db.inventory.find( { $or: [ { status: "A" }, { qty: { $lt: 30 } } ] } )
相当于SQL
SELECT * FROM inventory WHERE status = "A" OR qty < 30

> db.logs.find({ $or:[{'date' : '2019-06-25'},{'content':'crash'}]});
{ "_id" : ObjectId("5cd0983de8271827134eeb37"), "date" : "2019-06-19", "content" : "crash" }
{ "_id" : ObjectId("5cd0c9a4c33b2d6f4c83018d"), "date" : "2019-06-25", "content" : "warning" }
> 

5.AND和OR条件查询

db.inventory.find( {
     status: "A",
     $or: [ { qty: { $lt: 30 } }, { item: /^p/ } ]
} )
相当于SQL
SELECT * FROM inventory WHERE status = "A" AND ( qty < 30 OR item LIKE "p%")