Mastering Hierarchical Queries in Oracle SQL

Unraveling Tree Structures with Hierarchical Queries in Oracle SQL

Overview: Introduction to hierarchical data (e.g., employee-manager). Explain CONNECT BY, PRIOR, and LEVEL.

SQL> ed
  1  SELECT
  2      empno,
  3      ename,
  4      mgr,
  5      LEVEL AS hierarchy_level
  6  FROM
  7      emp
  8  START WITH
  9      mgr IS NULL
 10  CONNECT BY
 11*     PRIOR empno = mgr
SQL> /

   EMPNO ENAME         MGR    HIERARCHY_LEVEL
________ _________ _______ __________________
    7839 KING                               1
    7566 JONES        7839                  2
    7788 SCOTT        7566                  3
    7698 BLAKE        7839                  2
    7499 ALLEN        7698                  3
    7521 WARD         7698                  3
    7844 TURNER       7698                  3
    7782 CLARK        7839                  2
    7934 MILLER       7782                  3

9 rows selected.

Use Case: Visualizing an organizational chart or category tree.