As the title.
2. code.
In the database, the records of the parent-child relationship are often processed. In Oracle, you can use the query statement to fetch all the child records at one time. For example:
t1
t11
t111
t1111
t12
t121
t1211
The db data fields are as follows:
task_id task_name t.parent_task_id ***
*** *** *** ***
000001 t1 *** ***
000002 t11 000001 ***
000005 t12 000001 ***
000003 t111 000002 ***
000004 t1111 000003 ***
000006 t121 000005 ***
000007 t1211 000006 ***
*** *** *** ***
check sentence:
select t.task_id ,t.task_name ,t.parent_task_id
from t_task t
start with task_id='000001'
connect by prior task_id = parent_task_id;
The results show that:
task_id task_name t.parent_task_id
000001 t1
000002 t11 000001
000003 t111 000002
000004 t1111 000003
000005 t12 000001
000006 t121 000005
000007 t1211 000006
strat with specifies the condition for the start of the hierarchy, that is, the row that satisfies this condition can be used as the top level of the hierarchy tree
connect by prior refers to the association condition between layers, that is, what kind of row is the child row of the upper layer row (self-connection condition)
select level ,id,name,parentid from temptable2
connect by prior parentid (column belonging to top level) = id (column of child level) start with id =1
2. Note:
PRIOR is placed in front of the connect equal sign to search from the top level down. If it is placed after the equal sign, such as =PRIOR id, it can be searched from the bottom up, which can be used to implement a statement to find the top or bottom layer.
From: http://blog.sina.com.cn/s/blog_46d93f190101h7y6.html