Question

PostgreSQL Self Join

Asked by: jpadkins49

All I have a table in a postgre database that I have inherited that contains records that self join. It is a heirarchy tree for supervisors and employees.
The sample table layout is below:
tree_id   Parent_id  Object_id
1             0               349
1             349           346
1             346            355

The parent_id column is exactly how it sounds. It is the parent of the employee(e.g. manager). The object id is the employee number from the employees table. I need to write a self join query that pulls the heirarchy of the currently employee. For instance if I search by object_id=355, then it will pull all relations up to parent id of zero. So it will pull 346 and 349 from the database also. If you have a parent id of 0, then you are at the top of the heirarchy for that department. I am using this for a mailing notification feature for a leave module that I have developed, but I am unsure on how to get the data that I need via sql. I am not exactly sure I can even pull the data that I need via SQL. Any help will be greatly appreciated.

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Asked On
2009-03-26 at 06:00:37ID24267045
Topics

PostgreSQL Database

,

WebApplications

Participating Experts
2
Points
500
Comments
4

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Answers

 

by: ivanovnPosted on 2009-03-26 at 07:32:16ID: 23990801

You could probably write a recursive function that would obtain your values. Here is a quick untested example that you can use to get started. Notice that this recursive function inserts the results into a result table. You could probably get it to return results in a more friendly fashion.

CREATE OR REPLACE FUNCTION test(integer) RETURNS integer AS
$BODY$
 
DECLARE 
        rec record;
BEGIN
        -- Clear the previous results
	TRUNCATE TABLE test_result;
 
	FOR rec IN SELECT parent_id FROM test WHERE object_id=$1
 
	LOOP
                -- Base case: when you reach parent_id=0
                -- You need a base case to avoid infinite recursion
		IF rec.parent_id=0 THEN
			EXIT;
		ELSE
                        -- Recursive call
			EXECUTE 'INSERT INTO test_result SELECT test(' || rec.parent_id || ')';
		END IF;
 
	END LOOP;
 
	RETURN rec.parent_id;
 
END;
 
$BODY$
LANGUAGE 'plpgsql' VOLATILE;
 
 
-- The call to the function should be:
INSERT INTO test_result SELECT test(355);

                                              
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by: earthman2Posted on 2009-03-26 at 10:04:31ID: 23992686

CREATE OR REPLACE FUNCTION line_of_command( IN the_id  int ) RETURNS SETOF int AS $$
DECLARE
  the_parent_id int := the_id;
  level int := 0;
BEGIN
   WHILE  the_parent_id <> 0 AND level < 300  LOOP  -- beware of loop in data references
       RETURN NEXT the_parent_id;
       SELECT Parent_id INTO the_parent_id FROM  your_table_name_goes_here WHERE Object_id = the_parent_id;
       level := level + 1;
  END LOOP;  
  RETURN;
END;
$$ LANGUAGE plpgsql volatile strict;


#> select * from line_of_command( 355 );

postgresq 8.4 has new WITH .. SELECT syntax and windowing functions that could be used

 

by: earthman2Posted on 2009-03-28 at 10:12:38ID: 24009299

dev=> WITH RECURSIVE linocommand( parent_id, level, object_id, cycle ) AS (
  SELECT g.parent_id, 1, object_id, true FROM mgr g WHERE object_id = 355
UNION ALL
  SELECT g.parent_id, sg.level+1, g.object_id, g.parent_id <> 0 FROM mgr g, linocommand sg
  WHERE sg.parent_id = g.object_id and cycle
)
SELECT * FROM linocommand;
 parent_id | level | object_id | cycle
-----------+-------+-----------+-------
       346 |     1 |       355 | t
       349 |     2 |       346 | t
         0 |     3 |       349 | f
(3 rows)

dev=> WITH RECURSIVE linocommand( parent_id, level, object_id, cycle ) AS (
  SELECT g.parent_id, 1, object_id, true FROM mgr g WHERE object_id = 355
UNION ALL
  SELECT g.parent_id, sg.level+1, g.object_id, g.parent_id <> 0 FROM mgr g, linocommand sg
  WHERE sg.parent_id = g.object_id and cycle
)
SELECT object_id FROM linocommand;
 object_id
-----------
       355
       346
       349
(3 rows)

 

by: jpadkins49Posted on 2009-04-08 at 06:42:41ID: 31562955

Thanks again earthman2.

20120131-EE-VQP-002

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