좀더 나은 나를 위하여

조회하고자 하는 데이터의 특성상 가장 최근의 데이터부터 역순으로 인덱스를 조회하는 것이 유리할 경우가 있다.

예)

신입사원의 입사정보조회

게시판의 최신 글 내용 조회

로그성 데이터의 정보조회

내림차순인덱스 생성하는 방법

CREATE INDEX 인덱스명 ON BIG_EMP (EMPNO DESC)

조회시 힌트를 사용하는 방법

SELECT /*+ INDEX_DESC  (BIG_EMP 인덱스명) */

EMPNO FROM BIG_EMP ROWNUM<10 ;

--1 DESTINCT

SELECT

  DISTINCT A.DEPARTMENT_NAME

FROM

  DEPARTMENTS A

  , EMPLOYEES B

WHERE B.HIRE_DATE >= '20060101'

  AND B.DEPARTMENT_ID = A.DEPARTMENT_ID;

--2 INNER JOIN (ON)

SELECT

  DISTINCT A.DEPARTMENT_NAME

FROM

  DEPARTMENTS A INNER JOIN EMPLOYEES B

  ON B.DEPARTMENT_ID = A.DEPARTMENT_ID

WHERE B.HIRE_DATE >= '20060101';

--3 NATURAL JOIN

SELECT

  DISTINCT DEPARTMENT_NAME

FROM DEPARTMENTS A NATURAL JOIN EMPLOYEES B

WHERE B.HIRE_DATE >= '20060101';

--4 NATURAL JOIN (USING)

SELECT

  DISTINCT DEPARTMENT_NAME

FROM DEPARTMENTS A JOIN EMPLOYEES B

USING (DEPARTMENT_ID)

WHERE B.HIRE_DATE >= '20060101';

--5 SUBQUERY (IN)

SELECT

  DISTINCT DEPARTMENT_NAME

FROM DEPARTMENTS

WHERE DEPARTMENT_ID IN (SELECT DEPARTMENT_ID

                       FROM EMPLOYEES

                       WHERE HIRE_DATE >= '20060101');

--6 SUBQUERY (IN - GROUP)

SELECT

  A.DEPARTMENT_NAME

FROM DEPARTMENTS A

WHERE DEPARTMENT_ID IN (SELECT DEPARTMENT_ID

                       FROM EMPLOYEES

                       WHERE HIRE_DATE >= '20060101'

                       GROUP BY DEPARTMENT_ID

                       );

--7 SUBQUERY (ANY)

SELECT

  DISTINCT DEPARTMENT_NAME

FROM DEPARTMENTS

WHERE DEPARTMENT_ID = ANY (SELECT DEPARTMENT_ID

                       FROM EMPLOYEES

                       WHERE HIRE_DATE >= '20060101');

--8 SUBQUERY (SOME)

SELECT

  DISTINCT DEPARTMENT_NAME

FROM DEPARTMENTS

WHERE DEPARTMENT_ID = SOME (SELECT DEPARTMENT_ID

                       FROM EMPLOYEES

                       WHERE HIRE_DATE >= '20060101');

--9 SUBQUERY (EXITST)

SELECT

  A.DEPARTMENT_NAME

FROM DEPARTMENTS A

WHERE EXISTS(

  SELECT 'X' FROM EMPLOYEES

  WHERE HIRE_DATE >= '20060101'

    AND DEPARTMENT_ID = A.DEPARTMENT_ID

    );

--10 SUBQUERY (연관서브쿼리)

SELECT

  A.DEPARTMENT_NAME

FROM DEPARTMENTS A

WHERE DEPARTMENT_ID IN (

  SELECT DEPARTMENT_ID FROM EMPLOYEES

  WHERE HIRE_DATE >= '20060101'

    AND DEPARTMENT_ID = A.DEPARTMENT_ID

    );

--11 Scalar subquery

SELECT

  DISTINCT

(SELECT DEPARTMENT_NAME FROM  DEPARTMENTS A WHERE  A.DEPARTMENT_ID = B.DEPARTMENT_ID) AS DEPARTMENT_NAME

FROM EMPLOYEES B

WHERE  B.HIRE_DATE >= '20060101'

AND B.DEPARTMENT_ID IS NOT NULL;

--12 Scalar subquery + FROM 절 (GROUP BY)

SELECT

  (SELECT DEPARTMENT_NAME FROM  DEPARTMENTS A WHERE  A.DEPARTMENT_ID = B.DEPARTMENT_ID) AS DEPARTMENT_NAME

FROM (SELECT DEPARTMENT_ID

      FROM EMPLOYEES

      WHERE HIRE_DATE >= '20060101'

      GROUP BY DEPARTMENT_ID) B

WHERE  B.DEPARTMENT_ID IS NOT NULL;

--13 Scalar subquery + FROM 절 (DISTINCT)

SELECT

  (SELECT DEPARTMENT_NAME FROM  DEPARTMENTS A WHERE  A.DEPARTMENT_ID = B.DEPARTMENT_ID) AS DEPARTMENT_NAME

FROM (SELECT DISTINCT DEPARTMENT_ID

      FROM EMPLOYEES

      WHERE HIRE_DATE >= '20060101'

      ) B

WHERE  B.DEPARTMENT_ID IS NOT NULL;

--14 FROM절

SELECT

  DISTINCT A.DEPARTMENT_NAME

FROM DEPARTMENTS A , (SELECT DEPARTMENT_ID

                       FROM EMPLOYEES

                       WHERE HIRE_DATE >= '20060101') B

WHERE A.DEPARTMENT_ID = B.DEPARTMENT_ID ;

--15 FROM절 (DISTINCT)

SELECT

  A.DEPARTMENT_NAME

FROM DEPARTMENTS A , (SELECT DISTINCT DEPARTMENT_ID

                       FROM EMPLOYEES

                       WHERE HIRE_DATE >= '20060101') B

WHERE A.DEPARTMENT_ID = B.DEPARTMENT_ID ;

--16 FROM절 (GROUP BY)

SELECT

  A.DEPARTMENT_NAME

FROM DEPARTMENTS A , (SELECT DEPARTMENT_ID

                       FROM EMPLOYEES

                       WHERE HIRE_DATE >= '20060101'

                       GROUP BY DEPARTMENT_ID) B

WHERE A.DEPARTMENT_ID = B.DEPARTMENT_ID ;

--17 FROM절 (GROUP BY)

SELECT

  A.DEPARTMENT_NAME

FROM DEPARTMENTS A , (SELECT DEPARTMENT_ID

                       FROM EMPLOYEES

                       WHERE HIRE_DATE >= '20060101') B

WHERE A.DEPARTMENT_ID = B.DEPARTMENT_ID

GROUP BY A.DEPARTMENT_NAME;

--18 HAVING절

SELECT

  A.DEPARTMENT_NAME

FROM DEPARTMENTS A

GROUP BY A.DEPARTMENT_NAME, A.DEPARTMENT_ID

HAVING A.DEPARTMENT_ID IN (SELECT DEPARTMENT_ID

                       FROM EMPLOYEES

                       WHERE HIRE_DATE >= '20060101');

--19 GROUP BY

SELECT

   A.DEPARTMENT_NAME

FROM

  DEPARTMENTS A

  , EMPLOYEES B

WHERE B.HIRE_DATE >= '20060101'

  AND B.DEPARTMENT_ID = A.DEPARTMENT_ID

GROUP BY A.DEPARTMENT_NAME;

--20 ROWNUM         (젤빠름)

SELECT

  A.DEPARTMENT_NAME

FROM DEPARTMENTS A

WHERE DEPARTMENT_ID IN (

  SELECT DEPARTMENT_ID FROM EMPLOYEES

  WHERE HIRE_DATE >= '20060101'

    AND DEPARTMENT_ID = A.DEPARTMENT_ID

    AND ROWNUM <= 1

    );

더 있으면 알려주시요^^

절차형이 아니고 집합적적으로 생각하라.

정적 파티션과 동적파티션

정적파티션이 흔히 말하는 파티셔닝 테이블이다.

Skew 현상
데이터의 대량 삭제시 인덱스구조가 한쪽으로 쏠리는 현상

정기적으로 리빌드해주는것을 추천

블럭체이닝

다이나믹SQL , 스태틱SQL

스태틱SQL은 매번 SQL을 파싱하여 최적화하는 단계를 거침

다이나믹 SQL 은 컬럼등을 변수처리하여 파싱 및 최적화 단계를 건너뜀

Redo log

DB 장애등의 원복시 사용, Rollback 때도 아마 사용

http://www.techonthenet.com/sql/index.php

http://www.techonthenet.com/oracle/index.php

공부해올것