当树形控件的数据具大时，要加载整棵树，需要花费很多时间，此间，界面会无法响应，因此为改善用户体验，只需将树设置成“逐级加载”，也即按需加载。每次只加载一级数据。
在定义“逐级加载”树的ＳＱＬ语句时，需额外提供一个名为childrencount的字段，它用来表明该节点是否具有子节点。
高级应用：显示部门人员树，当部门人员例如多时，需采用逐级加载。
其中ＳＱＬ定义如下
(Oracle版)
select 'group-'||cast(id as varchar2(30)) as id , 'group-'||cast(pid as varchar2(30)) as pid ,name as caption , 'group-'||cast(id as varchar2(30)) as value ,1 as childrencount from oa_mygroup where userid=0 union all select 'user-'||cast(id as varchar2(30)) as id , 'group-'||cast(groupid as varchar2(30)) as pid , name as caption , 'user-'||cast(id as varchar2(30)) as value ,0 as childrencount from news_user(SQL Server版
select 'group-'||cast(id as varchar(30)) as id , 'group-'+cast(pid as varchar(30)) as pid ,name as caption , 'group-'+cast(id as varchar(30)) as value ,1 as childrencount from oa_mygroup where userid=0 union all select 'user-'+cast(id as varchar(30)) as id , 'group-'+cast(groupid as varchar(30)) as pid , name as caption , 'user-'+cast(id as varchar(30)) as value ,0 as childrencount from news_user
树根的值定义为：group-0
可以试着将“逐级加载”勾选上，以及不勾选上，看看性能对比