四、查詢操作
1、查詢所有記錄
db.userInfo.find();
相當于：select* from userInfo;
2、查詢去掉后的當前聚集集合中的某列的重復數據
db.userInfo.distinct("name");會過濾掉name中的相同數據
相當于：select disttince name from userInfo;
3、查詢age = 22的記錄
db.userInfo.find({"age": 22});
相當于： select * from userInfo where age = 22;
4、查詢age > 22的記錄
db.userInfo.find({age: {$gt: 22}});
相當于：select * from userInfo where age >22;
5、查詢age < 22的記錄
db.userInfo.find({age: {$lt: 22}});
相當于：select * from userInfo where age <22;
6、查詢age >= 25的記錄
db.userInfo.find({age: {$gte: 25}});
相當于：select * from userInfo where age >= 25;
7、查詢age <= 25的記錄
db.userInfo.find({age: {$lte: 25}});
相當于：select * from userInfo where age <= 25;
8、查詢age >= 23 并且 age <= 26
db.userInfo.find({age: {$gte: 23, $lte: 26}});
相當于：select * from userInfo where age >=23 and age <= 26;
9、查詢name中包含 mongo的數據
db.userInfo.find({name: /mongo/});
相當于：select * from userInfo where name like ‘%mongo%';
10、查詢name中以mongo開頭的
db.userInfo.find({name: /^mongo/});
相當于：select * from userInfo where name like ‘mongo%';
11、查詢指定列name、age數據
db.userInfo.find({}, {name: 1, age: 1});
相當于：select name, age from userInfo;
當然name也可以用true或false,當用ture的情況下河name:1效果一樣，如果用false就是排除name，顯示name以外的列信息。
12、查詢指定列name、age數據, age > 25
db.userInfo.find({age: {$gt: 25}}, {name: 1, age: 1});
相當于：select name, age from userInfo where age >25;
13、按照年齡排序
升序：db.userInfo.find().sort({age: 1});
降序：db.userInfo.find().sort({age: -1});
14、查詢前5條數據
db.userInfo.find().limit(5);
相當于：select * from (select * from userInfo) where rownum < 6;//oracle
select * from userInfo limit 5;//mysql
15、查詢10條以后的數據
db.userInfo.find().skip(10);
相當于：select * from userInfo where id not in (select id from (select * from userInfo) where? and rownum < 11);
16、查詢在5-10之間的數據
db.userInfo.find().limit(10).skip(5);
可用于分頁，limit是pageSize，skip是第幾頁*pageSize
17、or與 查詢
db.userInfo.find({$or: [{age: 22}, {age: 25}]});
相當于：select * from userInfo where age = 22 or age = 25;
18、查詢第一條數據
db.userInfo.findOne();
db.userInfo.find().limit(1);
相當于：select * from (select * from userInfo) where? and rownum < 2
19、查詢某個結果集的記錄條數
db.userInfo.find({age: {$gte: 25}}).count();
相當于：select count(*) from userInfo where age >= 20;
