[SQL]-(077) 서브 쿼리 사용하기7

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[Reference] 초보자를 위한 SQL 200제

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[SQL 문법]

서브 쿼리로 단일 값을 조회할 수 있다.

SELECT ename, sal, (select max(sal) from emp where job='SALESMAN') as MAXSAL,
                   (select min(sal) from emp where job='SALESMAN') as MINSAL
  FROM emp
  WHERE job='SALESMAN'

[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 ename, sal, (select max(sal) from emp where job='SALESMAN') as MAXSAL,
                   (select min(sal) from emp where job='SALESMAN') as MINSAL
  FROM emp
  WHERE job='SALESMAN'
"""
)

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]

    ENAME     SAL  MAXSAL  MINSAL
0  MARTIN  1250.0    1600    1250
1   ALLEN  1600.0    1600    1250
2  TURNER  1500.0    1600    1250
3    WARD  1250.0    1600    1250