여러 파일 중 첫번째 결과값만 가져오는 쿼리문 (상관관계 서브 쿼리)

상관관계 서브쿼리 : main 쿼리의 특정 컬럼의 기본키 데이터가 sub쿼리의 조건으로 사용되고 sub쿼리의 select 결과
 다시 main쿼리의 조건으로 서로 사용됨

SELECT *
FROM ATTACH
WHERE GLOBAL_CODE='P591';

SELECT * FROM ATTACH WHERE GLOBAL_CODE='P591'; 결과

SELECT MIN(B.SEQ)
FROM ATTACH B, ATTACH A
WHERE B.GLOBAL_CODE=A.GLOBAL_CODE

SELECT MIN(B.SEQ) FROM ATTACH B, ATTACH A WHERE B.GLOBAL_CODE=A.GLOBAL_CODE; 결과창

 

SELECT
    A.global_code,
    A.seq,
    A.filename,
    A.file_size,
    A.content_type,
    A.reg_date
FROM
    attach A
WHERE    
    A.global_code='P591'
    AND A.SEQ=1
    ;

 

원본

--상관관계 서브쿼리
SELECT
    A.global_code,
    A.seq,
    A.filename,
    A.file_size,
    A.content_type,
    A.reg_date
FROM
    attach A
WHERE    
    A.global_code='P591'
    AND A.SEQ=(
        SELECT MIN(B.SEQ)
        FROM ATTACH B
        WHERE B.GLOBAL_CODE=A.GLOBAL_CODE
    )
    ;