删除数据库
drop database dbName，
但有时候会碰到error，提示DB in use（cannot drop database XXX because it is currently in use）
solution：
use master
go
alter database dbName set single_user with rollback immediate ///将数据库回滚到原始配置状态
go
drop database dbName
drop database dbName，
但有时候会碰到error，提示DB in use（cannot drop database XXX because it is currently in use）
solution：
use master
go
alter database dbName set single_user with rollback immediate ///将数据库回滚到原始配置状态
go
drop database dbName
