# MongoDB数据表基本操作
## 查看全部数据表
```bash
> use ChatRoom
switched to db ChatRoom
> show collections
Account
Chat
system.indexes
system.users
```
## 创建数据表
```bash
> db.createCollection("Account")
{"ok":1}
> db.createCollection("Test",{capped:true, size:10000}) { "ok" : 1 }
{"ok":1}
```
-- 说明

capped:true，表示该集合的结构不能被修改；

size:在建表之初就指定一定的空间大小，接下来的插入操作会不断地按顺序APPEND数据在这个预分配好空间的文件中，如果已经超出空间大小，则回到文件头覆盖原来的数据继续插入。这种结构保证了插入和查询的高效性，它不允许删除单个记录，更新的也有限制：不能超过原有记录的大小。这种表效率很高，它适用于一些暂时保存数据的场合，比如网站中登录用户的session信息，又比如一些程序的监控日志，都是属于过了一定的时间就可以被覆盖的数据。

 

## 修改数据表名
```bash
> db.Account.renameCollection("Account1")
{ "ok" : 1 }
 ```

## 数据表帮助主题help
```bash
> db.Account.help()
DBCollection help
        db.Account.find().help() - show DBCursor help
        db.Account.count()
        db.Account.dataSize()
        db.Account.distinct( key ) - eg. db.Account.distinct( 'x' )
        db.Account.drop() drop the collection
        db.Account.dropIndex(name)
        db.Account.dropIndexes()
        db.Account.ensureIndex(keypattern[,options]) - options is an object with these possible fields: name, unique, dropDups
        db.Account.reIndex()
        db.Account.find([query],[fields]) - query is an optional query filter. fields is optional set of fields to retur.

                                                      e.g. db.Account.find( {x:77} , {name:1, x:1} )
        db.Account.find(...).count()
        db.Account.find(...).limit(n)
        db.Account.find(...).skip(n)
        db.Account.find(...).sort(...)
        db.Account.findOne([query])
        db.Account.findAndModify( { update : ... , remove : bool [, query: {}, sort: {}, 'new': false] } )
        db.Account.getDB() get DB object associated with collection
        db.Account.getIndexes()
        db.Account.group( { key : ..., initial: ..., reduce : ...[, cond: ...] } )
        db.Account.mapReduce( mapFunction , reduceFunction , <optional params> )
        db.Account.remove(query)
        db.Account.renameCollection( newName , <dropTarget> ) renames the collection.
        db.Account.runCommand( name , <options> ) runs a db command with the given name where the first param is the collection name
        db.Account.save(obj)
        db.Account.stats()
        db.Account.storageSize() - includes free space allocated to this collection
        db.Account.totalIndexSize() - size in bytes of all the indexes
        db.Account.totalSize() - storage allocated for all data and indexes
        db.Account.update(query, object[, upsert_bool, multi_bool])
        db.Account.validate() - SLOW
        db.Account.getShardVersion() - only for use with sharding 
```

## 查看全部表记录
```bash
> db.Account.find()
{ "_id" : ObjectId("4df08553188e444d001a763a"), "AccountID" : 1, "UserName" : "libing", "Password" : "1", "Age" : 26, "Email" : "libing@126.com", "RegisterDate" : "2011-06-09 16:31:25" }
{ "_id" : ObjectId("4df08586188e444d001a763b"), "AccountID" : 2, "UserName" : "lb", "Password" : "1", "Age" : 25, "Email" : "libing@163.com", "RegisterDate" : "2011-06-09 16:36:95" }
```