mongodb一些常用query指令

mongoDB的備份

./mongodump -h 127.0.0.1  -d dbname -c collectionName -o bakDir

mongoDB的query語句：

select：

      db.users.find({})

      db.users.find({'last_name': 'Smith'})

 field selection：

    //隻取ssn  相當于 select ssn from db where last_name == 'Smith'

    // retrieve ssn field for documents where last_name == 'Smith':

    db.users.find({last_name: 'Smith'}, {'ssn': 1});

    //除了域 thumbnail ，其他的域都取

    // retrieve all fields *except* the thumbnail field, for all documents:

    db.users.find({}, {thumbnail:0});

Sorting

MongoDB queries can return sorted results. To return all documents and sort by last name in ascending order, we'd query like so:

db.users.find({}).sort({last_name: 1});
           

{last_name: 1} 升序    
{last_name: 0} 降序
           

Skip and Limit

MongoDB also supports skip and limit for easy paging. Here we skip the first 20 last names, and limit our result set to 10:

db.users.find().skip(20).limit(10);
db.users.find({}, {}, 10, 20); // same as above, but less clear