How to traverse Hierarchical data in Oracle?

Problem Statement: You need to traverse the hierarchy data from top to bottom marking the level of each row in the hierarchy.

Solution:

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 professor and their professor’s professor(i.e. Dean), and so on, until the top manager/director of the institute.

Example 1: Identify the hierarchical/structure for the professor_id = 100 SQL:

/*      Function - Identify the hierarchical/structure for the professor_id = 102   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 = 102 CONNECT BY professor_id = PRIOR student_id;

Output

103 1   BROWN MICHAEL 104 2     -JONES WILLIAM 105 2     -MILLER DAVID 106 2     -DAVIS RICHARD 107 2     -GARCIA CHARLES

Example 2: Identify the hierarchical/structure where professor_id is NULL SQL:

/*      Function - Identify the hierarchical/structure professor_id is null   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;

Output : Few rows from above SQL

100 1   SMITH JAMES 101 2     -JOHNSON JOHN 108 3        -RODRIGUEZ JOSEPH 109 4           -WILSON THOMAS 110 4           -MARTINEZ CHRISTOPHER 111 4           -ANDERSON DANIEL 112 4           -TAYLOR PAUL 113 4           -THOMAS MARK 102 2     -WILLIAMS ROBERT 103 3        -BROWN MICHAEL 104 4           -JONES WILLIAM 105 4           -MILLER DAVID 106 4           -DAVIS RICHARD 107 4           -GARCIA CHARLES

Example 3: Identify the Institute entire hierarchical/structure SQL:

/*      Function - Identify the Institute entire hierarchical/structure   Tables Used - students          Data - documented below */ SELECT student_id,        level,        lpad('-',(level-1)*3) || first_name || ' ' || last_name AS full_name   FROM students CONNECT BY student_id = PRIOR professor_id;

Output: Few rows from above SQL

100 1   SMITH JAMES 101 1   JOHNSON JOHN 100 2     -SMITH JAMES 102 1   WILLIAMS ROBERT 100 2     -SMITH JAMES 103 1   BROWN MICHAEL 102 2     -WILLIAMS ROBERT 100 3        -SMITH JAMES 104 1   JONES WILLIAM 103 2     -BROWN MICHAEL 102 3        -WILLIAMS ROBERT 100 4           -SMITH JAMES 105 1   MILLER DAVID 103 2     -BROWN MICHAEL 102 3        -WILLIAMS ROBERT 100 4           -SMITH JAMES 106 1   DAVIS RICHARD 103 2     -BROWN MICHAEL 102 3        -WILLIAMS ROBERT 100 4           -SMITH JAMES 107 1   GARCIA CHARLES 103 2     -BROWN MICHAEL 102 3        -WILLIAMS ROBERT 100 4           -SMITH JAMES 108 1   RODRIGUEZ JOSEPH 101 2     -JOHNSON JOHN 100 3        -SMITH JAMES 109 1   WILSON THOMAS 108 2     -RODRIGUEZ JOSEPH 101 3        -JOHNSON JOHN 100 4           -SMITH JAMES 110 1   MARTINEZ CHRISTOPHER 108 2     -RODRIGUEZ JOSEPH 101 3        -JOHNSON JOHN 100 4           -SMITH JAMES 111 1   ANDERSON DANIEL 108 2     -RODRIGUEZ JOSEPH 101 3        -JOHNSON JOHN 100 4           -SMITH JAMES 112 1   TAYLOR PAUL 108 2     -RODRIGUEZ JOSEPH 101 3        -JOHNSON JOHN 100 4           -SMITH JAMES 113 1   THOMAS MARK 108 2     -RODRIGUEZ JOSEPH 101 3        -JOHNSON JOHN 100 4           -SMITH JAMES

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;