How to remove a branch with in a hierarchy of data in Oracle?

Problem Statement: You need to traverse the hierarchy data from top to bottom but doesn’t want a particular branch in the output.

Solution: We will look at couple of examples for this problem statement.

Oracle provides CONNECT BY clause to specify a hierarchical query i.e. how to connect the parent nodes and child nodes and the PRIOR operator to define the join condition/s between the parent nodes, and the LEVEL pseudo-column to indicate how far from the root/parent row the current row is.

Additionally, we can use the START WITH clause to indicate where to start the tree navigation. We must use the PRIOR operator to specify the column/s in the parent row that have the same values as the linking columns in the child row.

In order to loop through the entire hieratchy, remove the START WITH clause. This will fetch all the students with their managers, and their manager’s manager, and so on, until the top manager/director.

In this example, I will be using students data to demonstrate the solution for the problem statement.

Example

<p>SELECT student_id, first_name, last_name FROM students ; </p>

Output

<p>100 SMITH       JAMES
101 JOHNSON     JOHN
102 WILLIAMS    ROBERT
103 BROWN       MICHAEL
104 JONES       WILLIAM
105 MILLER      DAVID</p>

Assume you does not want to see “BROWN MICHAEL” and his subordinates in this report which means we need to remove/prune an entire branch from the tree. To do this, we must filter out the top of the branch to be removed in the CONNECT BY clause as an additional condition shown below.

SQL:

/*
     Function - Remove the branch - "BROWN MICHAEL" from the output
  Tables Used - students
         Data - Documented below
*/
SELECT student_id,
       level,
       lpad('-',(level-1)*3) || first_name || ' ' || last_name AS full_name
  FROM students
START WITH professor_id IS null
CONNECT BY professor_id = PRIOR student_id
AND NOT (first_name || ' ' || last_name = 'BROWN MICHAEL' )
ORDER SIBLINGS by first_name, last_name;

Output

<p>100 1   SMITH JAMES
101 2     -JOHNSON JOHN
108 3        -RODRIGUEZ JOSEPH
111 4           -ANDERSON DANIEL
110 4           -MARTINEZ CHRISTOPHER
112 4           -TAYLOR PAUL
113 4           -THOMAS MARK
109 4           -WILSON THOMAS
102 2     -WILLIAMS ROBERT</p>

if we want to just ignore the parent but still include the childs i.e. exclude only BROWN MICHAEL" but still include his subordinate students, the filter should be in the WHERE clause instead, as follows:

SQL:

/*
     Function - Remove only the branch head - BROWN MICHAEL from the output
  Tables Used - students
         Data - Documented below
*/
SELECT student_id,
       level,
       lpad('-',(level-1)*3) || first_name || ' ' || last_name AS full_name
  FROM students
WHERE NOT (first_name || ' ' || last_name = 'BROWN MICHAEL' )
START WITH professor_id IS null
CONNECT BY professor_id = PRIOR student_id
ORDER SIBLINGS by first_name, last_name;

Output

<p>100 1   SMITH JAMES
101 2     -JOHNSON JOHN
108 3        -RODRIGUEZ JOSEPH
111 4           -ANDERSON DANIEL
110 4           -MARTINEZ CHRISTOPHER
112 4           -TAYLOR PAUL
113 4           -THOMAS MARK
109 4           -WILSON THOMAS
102 2     -WILLIAMS ROBERT
106 4           -DAVIS RICHARD
107 4           -GARCIA CHARLES
104 4           -JONES WILLIAM</p>

Data Preparation: Data used for the problem is shown below. The data is completely made up for demonstration purpose.

Example

DROP TABLE students;
COMMIT;

CREATE TABLE students
    ( student_id     NUMBER(6)
    , first_name     VARCHAR2(20)
    , last_name      VARCHAR2(25)
    , email          VARCHAR2(40)
    , phone_number   VARCHAR2(20)
    , join_date      DATE
    , class_id       VARCHAR2(20)  
    , fees           NUMBER(8,2)
    , professor_id   NUMBER(6)
    , department_id  NUMBER(4)
    ) ;

Example

CREATE UNIQUE INDEX stu_id_pk ON students (student_id) ;
INSERT INTO students VALUES (100,'SMITH','JAMES','SMITH.JAMES@notreal.com','111.111.1245',TO_DATE('17-06-2003','DD-MM-YYYY'),'INS_CHAIRMAN',24000,NULL,NULL);
INSERT INTO students VALUES (101,'JOHNSON','JOHN','JOHNSON.JOHN@notreal.com','111.111.1246',TO_DATE('21-09-2005','DD-MM-YYYY'),'INS_VP',17000,100,90);
INSERT INTO students VALUES (102,'WILLIAMS','ROBERT','WILLIAMS.ROBERT@notreal.com','111.111.1247',TO_DATE('13-01-2001','DD-MM-YYYY'),'INS_VP',17000,100,90);
INSERT INTO students VALUES (103,'BROWN','MICHAEL','BROWN.MICHAEL@notreal.com','111.111.1248',TO_DATE('03-01-2006','DD-MM-YYYY'),'INS_STAFF',9000,102,60);
INSERT INTO students VALUES (104,'JONES','WILLIAM','JONES.WILLIAM@notreal.com','111.111.1249',TO_DATE('21-05-2007','DD-MM-YYYY'),'INS_STAFF',6000,103,60);
INSERT INTO students VALUES (105,'MILLER','DAVID','MILLER.DAVID@notreal.com','111.111.1250',TO_DATE('25-06-2005','DD-MM-YYYY'),'INS_STAFF',4800,103,60);
INSERT INTO students VALUES (106,'DAVIS','RICHARD','DAVIS.RICHARD@notreal.com','111.111.1251',TO_DATE('05-02-2006','DD-MM-YYYY'),'INS_STAFF',4800,103,60);
INSERT INTO students VALUES (107,'GARCIA','CHARLES','GARCIA.CHARLES@notreal.com','111.111.1252',TO_DATE('07-02-2007','DD-MM-YYYY'),'INS_STAFF',4200,103,60);
INSERT INTO students VALUES (108,'RODRIGUEZ','JOSEPH','RODRIGUEZ.JOSEPH@notreal.com','111.111.1253',TO_DATE('17-08-2002','DD-MM-YYYY'),'CL_PHY',12008,101,100);
INSERT INTO students VALUES (109,'WILSON','THOMAS','WILSON.THOMAS@notreal.com','111.111.1254',TO_DATE('16-08-2002','DD-MM-YYYY'),'CL_MATH',9000,108,100);
INSERT INTO students VALUES (110,'MARTINEZ','CHRISTOPHER','MARTINEZ.CHRISTOPHER@notreal.com','111.111.1255',TO_DATE('28-09-2005','DD-MM-YYYY'),'CL_MATH',8200,108,100);
INSERT INTO students VALUES (111,'ANDERSON','DANIEL','ANDERSON.DANIEL@notreal.com','111.111.1256',TO_DATE('30-09-2005','DD-MM-YYYY'),'CL_MATH',7700,108,100);
INSERT INTO students VALUES (112,'TAYLOR','PAUL','TAYLOR.PAUL@notreal.com','111.111.1257',TO_DATE('07-03-2006','DD-MM-YYYY'),'CL_MATH',7800,108,100);
INSERT INTO students VALUES (113,'THOMAS','MARK','THOMAS.MARK@notreal.com','111.111.1258',TO_DATE('07-12-2007','DD-MM-YYYY'),'CL_MATH',6900,108,100);

COMMIT;