mongdb的查询深入

查询多个条件（pretty是数据格式化）
>db.库名.find({key1:value1, key2:value2}).pretty()

案例：
> db.col.find({"by":"菜鸟教程", "title":"MongoDB 教程"}).pretty()
{
        "_id" : ObjectId("56063f17ade2f21f36b03133"),
        "title" : "MongoDB 教程",
        "description" : "MongoDB 是一个 Nosql 数据库",
        "by" : "菜鸟教程",
        "url" : "http://www.runoob.com",
        "tags" : [
                "mongodb",
                "database",
                "NoSQL"
        ],
        "likes" : 100
}类似SQL语句 WHERE by='菜鸟教程' AND title='MongoDB 教程'


OR 条件语句：
>db.库名.find(
   {
      $or: [
        {key1: value1}, {key2:value2}
      ]
   }
).pretty()

>db.col.find( { $or:[{"by":"菜鸟教程"},{"title": "MongoDB 教程"}] } ).pretty()
{
        "_id" : ObjectId("56063f17ade2f21f36b03133"),
        "title" : "MongoDB 教程",
        "description" : "MongoDB 是一个 Nosql 数据库",
        "by" : "菜鸟教程",
        "url" : "http://www.runoob.com",
        "tags" : [
                "mongodb",
                "database",
                "NoSQL"
        ],
        "likes" : 100
}AND和OR一起使用（SQL 语句为：'where likes>50 AND (by = '菜鸟教程' OR title = 'MongoDB 教程')'）

>db.col.find( { "likes": {$gt:50}, $or: [{"by": "菜鸟教程"},{"title": "MongoDB 教程"}] } ).pretty()
                 likes大于50并且（by等于菜鸟教程或者title等于MongDB教程）
 {
        "_id" : ObjectId("56063f17ade2f21f36b03133"),
        "title" : "MongoDB 教程",
        "description" : "MongoDB 是一个 Nosql 数据库",
        "by" : "菜鸟教程",
        "url" : "http://www.runoob.com",
        "tags" : [
                "mongodb",
                "database",
                "NoSQL"
        ],
        "likes" : 100
}