FMResultSet用来执行SQL语句结果的查询

FMDatabaseQueue用不同的线程来执行若干个查询和更新操作

FMDatabasePoolFMDatabaseQueue类似，但是只是用在数据库只读操作上

## FMResultSet

#### 逐行返回结果

- next方法本质是调用- nextWithErrorFMDB里面有的注释写的还是挺逗的，连wtf都有…哈哈

## FMDatabaseQueue

#### 事务处理

FMDatabase一样，也有事务的处理，分为exclusive事务和deferred事务

## FMDatabasePool

If you really really really know what you’re doing and FMDatabasePool is what you really really need (ie, you’re using a read only database), OK you can use it. But just be careful not to deadlock!