[SQL]-(089) 계층형 질의문으로 서열을 주고 데이터 출력하기1

---

[Reference] 초보자를 위한 SQL 200제

---

[SQL 문법]

데이터를 선택하여 계층 순서로 결과를 출력할 수 있다.

SELECT rpad(' ', level*3) || ename as employee, level, sal, job
  FROM emp
  START WITH ename='KING'
  CONNECT BY prior empno = mgr

[예시]

# 오라클 연동 및 접속
import pandas as pd
import cx_Oracle
dsn=cx_Oracle.makedsn('localhost',1521,'orcl')
db=cx_Oracle.connect('scott','tiger')
cursor=db.cursor()

# SQL 문법
cursor.execute("""
SELECT rpad(' ', level*3) || ename as employee, level, sal, job
  FROM emp
  START WITH ename='KING'
  CONNECT BY prior empno = mgr
"""
)

row=cursor.fetchall()
colname=cursor.description
col=[]

for i in colname:
    col.append(i[0])

# pandas를 사용한 데이터 프레임 형식으로 변환
emp=pd.DataFrame(row,columns=col)
print(emp)

[결과]

             EMPLOYEE  LEVEL     SAL        JOB
0                KING      1  5000.0  PRESIDENT
1               JONES      2  2975.0    MANAGER
2                FORD      3  3000.0    ANALYST
3               SMITH      4   800.0      CLERK
4               BLAKE      2  2850.0    MANAGER
5               ALLEN      3  1600.0   SALESMAN
6                WARD      3  1250.0   SALESMAN
7              MARTIN      3  1250.0   SALESMAN
8              TURNER      3  1500.0   SALESMAN
9               JAMES      3   950.0      CLERK
10              CLARK      2  2450.0    MANAGER
11             MILLER      3  1300.0      CLERK