//1、查询所有记录
db.userInfo.find();
//相当于：select * from userInfo;
//默认每页显示20条记录，当显示不下的情况下，可以用it迭代命令查询下一页数据。注意：键入it命令不能带"；”
//但是你可以设置每页显示数据的大小，用DBQuery.shellBatchSize = 50;这样每页就显示50条记录了。

//2、查询去掉后的当前聚集集合中的某列的重复数据
db.userInfo.distinct("name");
//会过滤掉name中的相同数据
//相当于：select distict name from userInfo;

//3、查询age = 22的记录
db.userInfo.find({"age": 22});
//相当于： select * from userInfo where age = 22;

//4、查询age > 22的记录
db.userInfo.find({age: {$gt: 22}});
//相当于：select * from userInfo where age > 22;

//5、查询age < 22的记录
db.userInfo.find({age: {$lt: 22}});
//相当于：select * from userInfo where age < 22;

//6、查询age >= 25的记录
db.userInfo.find({age: {$gte: 25}});
//相当于：select * from userInfo where age >= 25;

//7、查询age <= 25的记录
db.userInfo.find({age: {$lte: 25}});

//8、查询age >= 23 并且 age <= 26
db.userInfo.find({age: {$gte: 23, $lte: 26}});

//9、查询name中包含 mongo的数据
db.userInfo.find({name: /mongo/});
//相当于%%
//select * from userInfo where name like '%mongo%';

//10、查询name中以mongo开头的
db.userInfo.find({name: /^mongo/});
//select * from userInfo where name like 'mongo%';

//11、查询指定列name、age数据
db.userInfo.find({}, {name: 1, age: 1});
//相当于：select name, age from userInfo;
//当然name也可以用true或false,当用ture的情况下河name:1效果一样，如果用false就是排除name，显示name以外的列信息。

//12、查询指定列name、age数据, age > 25
db.userInfo.find({age: {$gt: 25}}, {name: 1, age: 1});
//相当于：select name, age from userInfo where age > 25;

//13、按照年龄排序
db.userInfo.find().sort({age: 1}); //升序
db.userInfo.find().sort({age: -1}); //降序

//14、查询name = zhangsan, age = 22的数据
db.userInfo.find({name: 'zhangsan', age: 22});
//相当于：select * from userInfo where name = 'zhangsan' and age = '22';

//15、查询前5条数据
db.userInfo.find().limit(5);
//相当于：select top 5 * from userInfo;

//16、查询10条以后的数据
db.userInfo.find().skip(10);
//相当于：select * from userInfo where id not in (select top 10 * from userInfo);

//17、查询在5-10之间的数据
db.userInfo.find().limit(10).skip(5);
//可用于分页，limit是pageSize，skip是第几页*pageSize

//18、or与 查询
db.userInfo.find({$or: [{age: 22}, {age: 25}]});
//相当于：select * from userInfo where age = 22 or age = 25;

//19、查询第一条数据
db.userInfo.findOne();
//相当于：select top 1 * from userInfo;
db.userInfo.find().limit(1);

//20、查询某个结果集的记录条数
db.userInfo.find({age: {$gte: 25}}).count();
//相当于：select count(*) from userInfo where age >= 20;

//21、按照某列进行排序
db.userInfo.find({sex: {$exists: true}}).count();
//相当于：select count(sex) from userInfo;

1、创建索引

db.userInfo.ensureIndex({name: 1});
db.userInfo.ensureIndex({name: 1, ts: -1});

2、查询当前聚集集合所有索引

db.userInfo.getIndexes();

3、查看总索引记录大小

db.userInfo.totalIndexSize();

4、读取当前集合的所有index信息

db.users.reIndex();

5、删除指定索引

db.users.dropIndex("name_1");

6、删除所有索引索引

db.users.dropIndexes();

tojson(new Object());
tojson(new Object('a'));

>var cursor = db.users.find();
> while (cursor.hasNext()) {
    printjson(cursor.next());
}

db.users.find().forEach(printjson);

既然可以当做数组处理，那么就可以获得它的长度：cursor.length();或者cursor.count(); 那样我们也可以用循环显示数据

for (var i = 0, len = c.length(); i < len; i++) printjson(c[i]);

> var arr = db.users.find().toArray();
> printjson(arr[2]);

db.users.find({age: {$lte: 28}}, {age: 1}).forEach(printjson);
db.users.find({age: {$lte: 28}}, {age: true}).forEach(printjson);

db.things.find({x:4}).forEach(function(x) {print(tojson(x));});