One article analyzing ORACLE tree structure query

This article brings you relevant knowledge about Oracle. It mainly introduces the article about parsing ORACLE tree structure query. The article expands on the topic in detail. Let’s take a look at it together. I hope Helpful to everyone.

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In our daily programming, we often encounter tree structures Represents, for example, organizational structures, administrative divisions, etc. These are often displayed through a table in the database. Here we take a simple administrative division table as an example. In actual use, other description fields and levels can be added to it.

#The table is associated with ID and PID to achieve tree structure storage. The table creation and data statements are as follows:

-- Create table
create table TREETEST
(
  id   NVARCHAR2(50),
  pid  NVARCHAR2(50),
  name NVARCHAR2(50)
)

insert into TREETEST (ID, PID, NAME) values ('1', null, '山东省');
insert into TREETEST (ID, PID, NAME) values ('2', '1', '青岛市');
insert into TREETEST (ID, PID, NAME) values ('3', '1', '烟台市');
insert into TREETEST (ID, PID, NAME) values ('4', null, '河南省');
insert into TREETEST (ID, PID, NAME) values ('5', null, '河北省');
insert into TREETEST (ID, PID, NAME) values ('6', '2', '市南区');
insert into TREETEST (ID, PID, NAME) values ('7', '2', '市北区');
insert into TREETEST (ID, PID, NAME) values ('8', '2', '即墨市');

How to query the tree structure? Oracle provides recursive query for query. The basic syntax is as follows:

SELECT [Column]…..
　　FEOM [Table]
　　WHERE Conditional1
　　START WITH Conditional2
　　CONNECT BY PRIOR Conditional3
　　ORDER BY [Column]

Description:

• Condition 1---Filter conditions, for all Returned records are filtered.
• Condition 2---The limiting condition of the root node. Of course, you can also relax the permissions to obtain multiple root nodes, that is, obtain multiple trees
• Condition 3---The link condition, the purpose is Give what is the relationship between father and son, and perform a recursive query based on this relationship (in the above table, ID=PID)
• Sort---Sort all returned records

Let’s look at specific examples below:

1. Query all sub-nodes under Shandong Province

SELECT *
  FROM TREETEST t
 START WITH t.PID=1
CONNECT BY PRIOR t.ID = t.PID

where the ID is 1 is the node of Shandong Province, and the query results are as follows:

#2. Query the next-level child node of Qingdao City (note the difference from the above, all Child nodes and next-level child nodes)

3. If you need to connect Qingdao City, Shandong Province, etc. to display, you can use SYS_CONNECT_BY_PATH to achieve this

SELECT t.ID, SYS_CONNECT_BY_PATH(t.NAME, '\') AS INDU_NAME
  FROM TREETEST t
 START WITH t.PID IS NULL
CONNECT BY PRIOR t.ID = t.PID

The query results are as follows:

4. In the same way, you can also proceed from bottom to top. Query

SELECT *
  FROM TREETEST t
 START WITH t.ID=8
CONNECT BY t.ID = PRIOR t.PID

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