SQL 전문가 가이드 (2013년)
- 쿼리 변환?
- 방식?
- 서브쿼리 Unnesting( SSU : Simple Subquery Unnesting ) ( 9i : Heuristic, 10g : Cost-Base )
- 서브쿼리 Unnesting
- 서브쿼리가 M쪽 집합이거나 Nonunique 인덱스일 때
- 3. 뷰 Merging
- 뷰 Merging이 불가능한 경우
- 4. 조건절 Pushing
- 가. 조건절(Predicate) Pushdown
- 나. 조건절( Predicate ) Pullup
- 다. 조인 조건( Join Predicate ) Pushdown
- 5. 조건절 이행
- 6. 불필요한 조인 제거
- 7. OR 조건을 Union으로 변환
- 8. 기타 쿼리 변환
- 가. 집합연산을 조인으로 변환
- 조인 칼럼에 IS NOT NULL 조건 추가
- 필터 조건 추가
쿼리 변환?
- 실행계획을 생성하고 비용을 계산하기에 앞서 사용자 SQL을 최적화에 유리한 형태로 재작성함
방식?
- 휴리스틱( Heuristic ) 쿼리 변환 : 일종의 규칙 기반의 최적화 기법( 불필요한 부분 제거 )
- 비용기반 쿼리 변환 : 변환된 쿼리의 비용이 더 낮을 때만 그것을 사용하고, 그렇지 않을 때는 원본 쿼리 그대로 두고 최적화를 수행한다.
서브쿼리 Unnesting( SSU : Simple Subquery Unnesting ) ( 9i : Heuristic, 10g : Cost-Base )
- 서브쿼리를 메인 쿼리와 같은 레벨로 풀어낸다면 다양한 액세스 경로와 조인 메소드를 평가 할 수 있다.
- 옵티마이저는 많은 조인 테크닉을 가지기 때문에 조인 형태로 변환했을 때 더 나은 실행계획을 찾을 가능성이 높아진다.
SQL> SELECT *
2 FROM EMP A
3 WHERE EXISTS(SELECT 'X' FROM DEPT WHERE DEPTNO = A.DEPTNO) -- JE( Join Elimination( hint : ELIMINATE_JOIN, NO_ELIMINATE_JOIN ) )
4 AND SAL > (SELECT AVG(SAL)
5 FROM EMP B
6 WHERE EXISTS(SELECT /*+ */ 'O'
7 FROM SALGRADE S
8 WHERE B.SAL BETWEEN LOSAL AND HISAL
9 AND GRADE = 4) );
-----------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |
-----------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 4 |00:00:00.01 | 16 | | | |
|* 1 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 1 | 4 |00:00:00.01 | 16 | | | |
|* 2 | INDEX FULL SCAN | FK_EMP | 1 | 14 | 14 |00:00:00.01 | 2 | | | |
| 3 | SORT AGGREGATE | | 1 | 1 | 1 |00:00:00.01 | 12 | | | |
| 4 | MERGE JOIN SEMI | | 1 | 14 | 5 |00:00:00.01 | 12 | | | |
| 5 | SORT JOIN | | 1 | 14 | 14 |00:00:00.01 | 6 | 2048 | 2048 | 2048 (0)|
| 6 | TABLE ACCESS FULL | EMP | 1 | 14 | 14 |00:00:00.01 | 6 | | | |
|* 7 | FILTER | | 14 | | 5 |00:00:00.01 | 6 | | | |
|* 8 | SORT JOIN | | 14 | 1 | 6 |00:00:00.01 | 6 | 2048 | 2048 | 2048 (0)|
| 9 | VIEW | VW_SQ_1 | 1 | 1 | 1 |00:00:00.01 | 6 | | | |
|* 10 | TABLE ACCESS FULL | SALGRADE | 1 | 1 | 1 |00:00:00.01 | 6 | | | |
-----------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("SAL">)
2 - filter("A"."DEPTNO" IS NOT NULL)
7 - filter("B"."SAL"<="ITEM_2")
8 - access(INTERNAL_FUNCTION("B"."SAL")>=INTERNAL_FUNCTION("ITEM_1"))
filter(INTERNAL_FUNCTION("B"."SAL")>=INTERNAL_FUNCTION("ITEM_1"))
10 - filter("GRADE"=4)
서브 쿼리의 처리의 옵티마이저의 선택..
- 조인문으로 변환 후 최적화( Subquery Unnesting == Subquery Flattening ) ( 다양한 실행계획 )
- 서브쿼리를 Unnesting 하지 않고 원래대로 둔 상태에서 최적화 한다.( Filter ) ( 제한적 실행계획 )
서브쿼리 Unnesting
- Filter
SQL> SELECT * FROM V$VERSION WHERE ROWNUM <= 1;
BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
-- JE( Join Elimination )ㅡㅡ^
SQL> SELECT COUNT(*)
2 FROM EMP
3 WHERE DEPTNO IN ( SELECT DEPTNO FROM DEPT );
-------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
-------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 1 |00:00:00.01 | 1 |
| 1 | SORT AGGREGATE | | 1 | 1 | 1 |00:00:00.01 | 1 |
|* 2 | INDEX FULL SCAN| FK_EMP | 1 | 14 | 14 |00:00:00.01 | 1 |
-------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter("DEPTNO" IS NOT NULL)
SQL> ALTER TABLE EMP DROP CONSTRAINT FK_DEPTNO;
테이블이 변경되었습니다.
-- FILTER
SQL> SELECT COUNT(*)
2 FROM EMP
3 WHERE DEPTNO IN ( SELECT /*+ NO_UNNEST */ DEPTNO FROM DEPT );
-----------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
-----------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 1 |00:00:00.01 | 9 |
| 1 | SORT AGGREGATE | | 1 | 1 | 1 |00:00:00.01 | 9 |
|* 2 | FILTER | | 1 | | 14 |00:00:00.01 | 9 |
| 3 | TABLE ACCESS FULL| EMP | 1 | 14 | 14 |00:00:00.01 | 6 |
|* 4 | INDEX UNIQUE SCAN| PK_DEPT | 3 | 1 | 3 |00:00:00.01 | 3 |
-----------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter( IS NOT NULL) <-- ??
4 - access("DEPTNO"=:B1) <-- 별도의 서브플랜으로 최적화..
SQL> EXPLAIN PLAN FOR
2 SELECT COUNT(*)
3 FROM EMP
4 WHERE DEPTNO IN ( SELECT /*+ NO_UNNEST */ DEPTNO FROM DEPT );
SQL> SELECT * FROM TABLE( DBMS_XPLAN.DISPLAY( NULL ) );
-------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 3 | 3 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | 3 | | |
|* 2 | FILTER | | | | | |
| 3 | TABLE ACCESS FULL| EMP | 14 | 42 | 3 (0)| 00:00:01 |
|* 4 | INDEX UNIQUE SCAN| PK_DEPT | 1 | 3 | 0 (0)| 00:00:01 |
-------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter( EXISTS (SELECT /*+ NO_UNNEST */ 0 FROM "DEPT" "DEPT"
WHERE "DEPTNO"=:B1))
4 - access("DEPTNO"=:B1)
- Unnesting 과정
-- 1. VIEW
SQL> SELECT /*+ NO_MERGE( A ) */ COUNT(*)
2 FROM (SELECT DEPTNO FROM DEPT) A, EMP B
3 WHERE A.DEPTNO = B.DEPTNO;
-------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | Reads |
-------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 1 |00:00:00.01 | 3 | 1 |
| 1 | SORT AGGREGATE | | 1 | 1 | 1 |00:00:00.01 | 3 | 1 |
| 2 | NESTED LOOPS | | 1 | 14 | 14 |00:00:00.01 | 3 | 1 |
| 3 | VIEW | | 1 | 4 | 4 |00:00:00.01 | 1 | 0 |
| 4 | INDEX FULL SCAN| PK_DEPT | 1 | 4 | 4 |00:00:00.01 | 1 | 0 |
|* 5 | INDEX RANGE SCAN| FK_EMP | 4 | 4 | 14 |00:00:00.01 | 2 | 1 |
-------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
5 - access("A"."DEPTNO"="B"."DEPTNO")
-- 2. MERGE
SQL> SELECT /*+ MERGE( A ) */ COUNT(*)
2 FROM (SELECT DEPTNO FROM DEPT) A, EMP B
3 WHERE A.DEPTNO = B.DEPTNO
4 ;
----------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
----------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 1 |00:00:00.01 | 3 |
| 1 | SORT AGGREGATE | | 1 | 1 | 1 |00:00:00.01 | 3 |
| 2 | NESTED LOOPS | | 1 | 14 | 14 |00:00:00.01 | 3 |
| 3 | INDEX FULL SCAN | PK_DEPT | 1 | 4 | 4 |00:00:00.01 | 1 |
|* 4 | INDEX RANGE SCAN| FK_EMP | 4 | 4 | 14 |00:00:00.01 | 2 |
----------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
4 - access("DEPTNO"="B"."DEPTNO")
-- 3. Unnesting
SQL> SELECT COUNT(*)
2 FROM EMP
3 WHERE DEPTNO IN ( SELECT DEPTNO FROM DEPT );
-------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | Reads |
-------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 1 |00:00:00.01 | 3 | 1 |
| 1 | SORT AGGREGATE | | 1 | 1 | 1 |00:00:00.01 | 3 | 1 |
| 2 | NESTED LOOPS | | 1 | 14 | 14 |00:00:00.01 | 3 | 1 |
| 3 | INDEX FULL SCAN | PK_DEPT | 1 | 4 | 4 |00:00:00.01 | 1 | 1 |
|* 4 | INDEX RANGE SCAN| FK_EMP | 4 | 4 | 14 |00:00:00.01 | 2 | 0 |
-------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
4 - access("DEPTNO"="DEPTNO")
- 최근 옵티마이저는 서브쿼리를 Unnesting했을 때 쿼리 수행 비용이 더 낮은지를 비교해 보고 적용 여부를 판단하는 쪽으로 발전하고 있다.
- unnest : 서브쿼리를 Unnestiong 함으로써 조인방식으로 최적화하도록 유도한다.
- no_unnest : 서브쿼리를 그대로 둔 상태에서 필터 방식으로 최적화하도록 유도한다.
서브쿼리가 M쪽 집합이거나 Nonunique 인덱스일 때
- (1) PK/Unique 제약 또는 Unique 인덱스가 없는 서브쿼리 쪽 테이블이 먼저 드라이빙된다면,
먼저 Sort unique 오퍼레이션을 수행함으로써 1쪽 집합으로 만든 다음에 조인한다. - (2) 메인 쿼리 쪽 테이블이 드라이빙된다면 세미 조인( Semi Join ) 방식으로 조인한다.
이것이 세미 조인(Semi Join)이 탄생하게 된 배경이다.
- <사례1>
SELECT *
FROM DEPT D
WHERE DEPTNO IN (SELECT DEPTNO FROM EMP E );
--(1) EMP 테이블 드라이빙
SQL> SELECT /*+ QB_NAME( MAIN ) LEADING( E@SUB ) */ *
2 FROM DEPT D
3 WHERE DEPTNO IN (SELECT /*+ QB_NAME( SUB ) UNNEST */ DEPTNO FROM EMP E );
-----------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |
-----------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 3 |00:00:00.01 | 6 | | | |
| 1 | NESTED LOOPS | | 1 | | 3 |00:00:00.01 | 6 | | | |
| 2 | NESTED LOOPS | | 1 | 3 | 3 |00:00:00.01 | 3 | | | |
| 3 | SORT UNIQUE | | 1 | 14 | 3 |00:00:00.01 | 1 | 2048 | 2048 | 2048 (0)|
| 4 | INDEX FULL SCAN | FK_EMP | 1 | 14 | 14 |00:00:00.01 | 1 | | | |
|* 5 | INDEX UNIQUE SCAN | PK_DEPT | 3 | 1 | 3 |00:00:00.01 | 2 | | | |
| 6 | TABLE ACCESS BY INDEX ROWID| DEPT | 3 | 1 | 3 |00:00:00.01 | 3 | | | |
-----------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
5 - access("DEPTNO"="DEPTNO")
--(2) DEPT 테이블 드라이브
SQL> SELECT /*+ QB_NAME( MAIN ) LEADING( D@SUB ) */ *
2 FROM EMP E
3 WHERE DEPTNO IN (SELECT /*+ QB_NAME( SUB ) UNNEST */ DEPTNO FROM DEPT D );
-------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |
-------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 14 |00:00:00.01 | 6 | | | |
| 1 | NESTED LOOPS | | 1 | | 14 |00:00:00.01 | 6 | | | |
| 2 | NESTED LOOPS | | 1 | 14 | 14 |00:00:00.01 | 4 | | | |
| 3 | SORT UNIQUE | | 1 | 4 | 4 |00:00:00.01 | 1 | 2048 | 2048 | 2048 (0)|
| 4 | INDEX FULL SCAN | DEPT_DEPTNO_IDX | 1 | 4 | 4 |00:00:00.01 | 1 | | | |
|* 5 | INDEX RANGE SCAN | FK_EMP | 4 | 5 | 14 |00:00:00.01 | 3 | | | |
| 6 | TABLE ACCESS BY INDEX ROWID| EMP | 14 | 4 | 14 |00:00:00.01 | 2 | | | |
-------------------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
5 - access("DEPTNO"="DEPTNO")
- <사례2>
SELECT *
FROM EMP E
WHERE DEPTNO IN (SELECT DEPTNO FROM DEPT D );
-- (1) DEPT 테이블 드라이브
SQL> ALTER TABLE DEPT DROP PRIMARY KEY;
테이블이 변경되었습니다.
SQL> CREATE INDEX DEPT_DEPTNO_IDX ON DEPT( DEPTNO );
인덱스가 생성되었습니다.
SQL> SELECT /*+ QB_NAME( MAIN ) LEADING( D@SUB ) */ *
2 FROM EMP E
3 WHERE DEPTNO IN (SELECT /*+ QB_NAME( SUB ) UNNEST */ DEPTNO FROM DEPT D );
-------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |
-------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 14 |00:00:00.01 | 6 | | | |
| 1 | NESTED LOOPS | | 1 | | 14 |00:00:00.01 | 6 | | | |
| 2 | NESTED LOOPS | | 1 | 14 | 14 |00:00:00.01 | 4 | | | |
| 3 | SORT UNIQUE | | 1 | 4 | 4 |00:00:00.01 | 1 | 2048 | 2048 | 2048 (0)|
| 4 | INDEX FULL SCAN | DEPT_DEPTNO_IDX | 1 | 4 | 4 |00:00:00.01 | 1 | | | |
|* 5 | INDEX RANGE SCAN | FK_EMP | 4 | 5 | 14 |00:00:00.01 | 3 | | | |
| 6 | TABLE ACCESS BY INDEX ROWID| EMP | 14 | 4 | 14 |00:00:00.01 | 2 | | | |
-------------------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
5 - access("DEPTNO"="DEPTNO")
-- (1) 위 쿼리 QT
SQL> SELECT /*+ LEADING( D ) */ *
2 FROM (SELECT /*+ NO_MERGE */ DISTINCT DEPTNO FROM DEPT D ) D, EMP E
3 WHERE E.DEPTNO = D.DEPTNO ;
----------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |
----------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 14 |00:00:00.01 | 11 | | | |
| 1 | NESTED LOOPS | | 1 | | 14 |00:00:00.01 | 11 | | | |
| 2 | NESTED LOOPS | | 1 | 14 | 14 |00:00:00.01 | 9 | | | |
| 3 | VIEW | | 1 | 4 | 4 |00:00:00.01 | 6 | | | |
| 4 | HASH UNIQUE | | 1 | 4 | 4 |00:00:00.01 | 6 | 1518K| 1518K| 874K (0)|
| 5 | TABLE ACCESS FULL | DEPT | 1 | 4 | 4 |00:00:00.01 | 6 | | | |
|* 6 | INDEX RANGE SCAN | FK_EMP | 4 | 5 | 14 |00:00:00.01 | 3 | | | |
| 7 | TABLE ACCESS BY INDEX ROWID| EMP | 14 | 4 | 14 |00:00:00.01 | 2 | | | |
----------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
6 - access("E"."DEPTNO"="D"."DEPTNO")
--(2) EMP 테이블 드라이브
SQL> SELECT /*+ QB_NAME( MAIN ) LEADING( E@MAIN ) */ *
2 FROM EMP E
3 WHERE DEPTNO IN (SELECT /*+ QB_NAME( SUB ) UNNEST */ DEPTNO FROM DEPT D );
------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 14 |00:00:00.01 | 9 |
| 1 | NESTED LOOPS SEMI | | 1 | 14 | 14 |00:00:00.01 | 9 |
| 2 | TABLE ACCESS FULL| EMP | 1 | 14 | 14 |00:00:00.01 | 7 |
|* 3 | INDEX RANGE SCAN | DEPT_DEPTNO_IDX | 3 | 4 | 3 |00:00:00.01 | 2 |
------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - access("DEPTNO"="DEPTNO")
3. 뷰 Merging
- <쿼리1>
SELECT *
FROM (SELECT * FROM EMP WHERE JOB = 'SALESMAN') A
, (SELECT * FROM DEPT WHERE LOC = 'CHICAGO') A
WHERE A.DEPTNO = B.DEPTNO
- <쿼리2>
SELECT *
FROM EMP A, DEPT B
WHERE A.DEPTNO = B.DEPTNO
AND A.JOB = 'SALESMAN'
AND B.LOC = 'CHICAGO'
- VIEW
-- 뷰 생성
SQL> CREATE OR REPLACE VIEW EMP_SALESMAN
2 AS
3 SELECT EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO
4 FROM EMP
5 WHERE JOB = 'SALESMAN';
-- NO_MERGE
SQL> SELECT /*+ NO_MERGE( E ) LEADING( E ) */ E.EMPNO, E.ENAME, E.JOB, E.MGR, E.SAL, D.DNAME
2 FROM EMP_SALESMAN E, DEPT D
3 WHERE D.DEPTNO = E.DEPTNO
4 AND E.SAL >= 1500;
----------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
----------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 2 |00:00:00.01 | 12 |
| 1 | NESTED LOOPS | | 1 | | 2 |00:00:00.01 | 12 |
| 2 | NESTED LOOPS | | 1 | 3 | 2 |00:00:00.01 | 10 |
| 3 | VIEW | EMP_SALESMAN | 1 | 3 | 2 |00:00:00.01 | 7 |
|* 4 | TABLE ACCESS FULL | EMP | 1 | 3 | 2 |00:00:00.01 | 7 |
|* 5 | INDEX RANGE SCAN | DEPT_DEPTNO_IDX | 2 | 1 | 2 |00:00:00.01 | 3 |
| 6 | TABLE ACCESS BY INDEX ROWID| DEPT | 2 | 1 | 2 |00:00:00.01 | 2 |
----------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
4 - filter(("JOB"='SALESMAN' AND "SAL">=1500))
5 - access("D"."DEPTNO"="E"."DEPTNO")
-- MERGE
SQL> SELECT /*+ MERGE( E ) LEADING( E ) USE_NL( D ) */ E.EMPNO, E.ENAME, E.JOB, E.MGR, E.SAL, D.DNAME
2 FROM EMP_SALESMAN E, DEPT D
3 WHERE D.DEPTNO = E.DEPTNO
4 AND E.SAL >= 1500;
----------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
----------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 2 |00:00:00.01 | 12 |
| 1 | NESTED LOOPS | | 1 | | 2 |00:00:00.01 | 12 |
| 2 | NESTED LOOPS | | 1 | 3 | 2 |00:00:00.01 | 10 |
|* 3 | TABLE ACCESS FULL | EMP | 1 | 3 | 2 |00:00:00.01 | 7 |
|* 4 | INDEX RANGE SCAN | DEPT_DEPTNO_IDX | 2 | 1 | 2 |00:00:00.01 | 3 |
| 5 | TABLE ACCESS BY INDEX ROWID| DEPT | 2 | 1 | 2 |00:00:00.01 | 2 |
----------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - filter(("JOB"='SALESMAN' AND "SAL">=1500))
4 - access("D"."DEPTNO"="DEPTNO")
- 위 같은 단순한 뷰는 Merging하더라도 성능이 나빠지지 않는다.
- 복잡한 연산을 포함하는 뷰는 Merging하면 오히려 성능이 더 나빠질 수 도있다.( group by 절, select-list에 distinct 연산자 포함 )
뷰 Merging이 불가능한 경우
- 집합 연산자( union, union all, intersect, minus )
- connect by절
- rownum pseudo 칼럼
- select-list에 집계 함수( avg, count, max, min, sum) 사용
SQL> SELECT /*+ OPTIMIZER_FEATURES_ENABLE('10.2.0.3') */ *
2 FROM DEPT D
3 , (SELECT DEPTNO, SUM( SAL ) AS SAL
4 FROM EMP E
5 GROUP BY DEPTNO ) E
6 WHERE D.LOC = 'DALLAS'
7 AND D.DEPTNO = E.DEPTNO ;
----------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |
----------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 1 |00:00:00.01 | 8 | | | |
| 1 | HASH GROUP BY | | 1 | 1 | 1 |00:00:00.01 | 8 | 817K| 817K| 484K (0)|
| 2 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 5 | 5 |00:00:00.01 | 8 | | | |
| 3 | NESTED LOOPS | | 1 | 5 | 7 |00:00:00.01 | 7 | | | |
|* 4 | TABLE ACCESS FULL | DEPT | 1 | 1 | 1 |00:00:00.01 | 6 | | | |
|* 5 | INDEX RANGE SCAN | FK_EMP | 1 | 5 | 5 |00:00:00.01 | 1 | | | |
----------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
4 - filter("D"."LOC"='DALLAS')
5 - access("D"."DEPTNO"="DEPTNO")
- 분석 함수( Analytic Function )
4. 조건절 Pushing
- 옵티마지어가 뷰를 처리함에 있어 1차적으로 뷰 Merging을 고려하지만, 조건절 Pushing을 시도할 수도 있다.
- 조건절(Predicate) Pushdown : 쿼리 블록 밖에 있는 조건절을 쿼리 블록 안쪽으로 밀어 넣는 것을 말함
- 조건절(Prediate) Pullup : 쿼리 블록 안에 있는 조건절을 쿼리 블록 밖으로 내오는 것을 말하며, 그것을 다시 다른 쿼리 블록에 PushDown 하는 데 사용함
- 조인 조건( Join Predicate) Pushdown : NL Join 수쟁 중에 드라이빙 테이블에서 읽은 값을 건건이 Inner 쪽( =right side) 뷰 쿼리 블록 안으로 밀어 넣는 것을 말함
가. 조건절(Predicate) Pushdown
- 쿼리 블록 밖에 있는 조건절을 쿼리 블록 안쪽으로 밀어 넣는 것을 말함
-- CASE 1
SQL> SELECT /*+ NO_MERGE( E ) */ DEPTNO, AVG_SAL
2 FROM (SELECT DEPTNO, AVG(SAL) AS AVG_SAL
3 FROM EMP
4 GROUP BY DEPTNO ) E
5 WHERE DEPTNO = 30;
--------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
--------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 1 |00:00:00.01 | 2 |
| 1 | VIEW | | 1 | 1 | 1 |00:00:00.01 | 2 |
| 2 | SORT GROUP BY NOSORT | | 1 | 1 | 1 |00:00:00.01 | 2 |
| 3 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 6 | 6 |00:00:00.01 | 2 |
|* 4 | INDEX RANGE SCAN | FK_EMP | 1 | 6 | 6 |00:00:00.01 | 1 |
--------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
4 - access("DEPTNO"=30)
-- CASE 2
SQL> SELECT D.DEPTNO, D.DNAME, E.AVG_SAL
2 FROM (SELECT DEPTNO, AVG(SAL) AS AVG_SAL
3 FROM EMP
4 GROUP BY DEPTNO) E
5 , DEPT D
6 WHERE D.DEPTNO = E.DEPTNO
7 AND D.DEPTNO = 30
--AND E.DEPTNO = 30 <-- 조건절 이행
8 ;
---------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |
---------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 1 |00:00:00.01 | 5 | | | |
| 1 | NESTED LOOPS | | 1 | 1 | 1 |00:00:00.01 | 5 | | | |
| 2 | TABLE ACCESS BY INDEX ROWID | DEPT | 1 | 1 | 1 |00:00:00.01 | 3 | | | |
|* 3 | INDEX RANGE SCAN | DEPT_DEPTNO_IDX | 1 | 1 | 1 |00:00:00.01 | 2 | | | |
| 4 | VIEW | | 1 | 1 | 1 |00:00:00.01 | 2 | | | |
| 5 | SORT GROUP BY | | 1 | 1 | 1 |00:00:00.01 | 2 | 2048 | 2048 | 2048 (0)|
| 6 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 6 | 6 |00:00:00.01 | 2 | | | |
|* 7 | INDEX RANGE SCAN | FK_EMP | 1 | 6 | 6 |00:00:00.01 | 1 | | | |
---------------------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - access("D"."DEPTNO"=30)
7 - access("DEPTNO"=30)
나. 조건절( Predicate ) Pullup
- 안쪽에 있는 조건들을 바깥 쪽으로 끄집어 내는것을 말함.
- 조건절( Predicate ) Pullup
SQL> SELECT *
2 FROM (SELECT DEPTNO, AVG(SAL) FROM EMP WHERE DEPTNO = 10 GROUP BY DEPTNO ) e1
3 , (SELECT DEPTNO, MIN(SAL), MAX(SAL) FROM EMP GROUP BY DEPTNO ) e2
4 WHERE E1.DEPTNO = E2.DEPTNO;
------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |
------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 1 |00:00:00.01 | 4 | | | |
|* 1 | HASH JOIN | | 1 | 1 | 1 |00:00:00.01 | 4 | 963K| 963K| 382K (0)|
| 2 | VIEW | | 1 | 1 | 1 |00:00:00.01 | 2 | | | |
| 3 | HASH GROUP BY | | 1 | 1 | 1 |00:00:00.01 | 2 | 899K| 899K| 720K (0)|
| 4 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 3 | 3 |00:00:00.01 | 2 | | | |
|* 5 | INDEX RANGE SCAN | FK_EMP | 1 | 3 | 3 |00:00:00.01 | 1 | | | |
| 6 | VIEW | | 1 | 1 | 1 |00:00:00.01 | 2 | | | |
| 7 | HASH GROUP BY | | 1 | 1 | 1 |00:00:00.01 | 2 | 838K| 838K| 722K (0)|
| 8 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 3 | 3 |00:00:00.01 | 2 | | | |
|* 9 | INDEX RANGE SCAN | FK_EMP | 1 | 3 | 3 |00:00:00.01 | 1 | | | |
------------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - access("E1"."DEPTNO"="E2"."DEPTNO")
5 - access("DEPTNO"=10)
9 - access("DEPTNO"=10)
- QT
SELECT *
FROM (SELECT DEPTNO, AVG(SAL) FROM EMP WHERE DEPTNO = 10 GROUP BY DEPTNO ) e1
, (SELECT DEPTNO, MIN(SAL), MAX(SAL) FROM EMP WHERE DEPTNO = 10 GROUP BY DEPTNO ) e2
WHERE E1.DEPTNO = E2.DEPTNO;
다. 조인 조건( Join Predicate ) Pushdown
- 조인 조건절을 뷰 쿼리 블록 안으로 밀어 넣는 것( NL JOIN )
- Oracle 11g
SQL> SELECT /*+ LEADING( D ) USE_NL( E ) NO_MERGE( E ) PUSH_PRED( E ) */ D.DEPTNO, D.DNAME, E.AVG_SAL
2 FROM DEPT D
3 , (SELECT DEPTNO, AVG(SAL) AVG_SAL FROM EMP GROUP BY DEPTNO ) E
4 WHERE E.DEPTNO(+) = D.DEPTNO;
------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |
------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 4 |00:00:00.01 | 11 | | | |
| 1 | NESTED LOOPS OUTER | | 1 | 4 | 4 |00:00:00.01 | 11 | | | |
| 2 | TABLE ACCESS FULL | DEPT | 1 | 4 | 4 |00:00:00.01 | 7 | | | |
| 3 | VIEW PUSHED PREDICATE | | 4 | 1 | 3 |00:00:00.01 | 4 | | | |
| 4 | SORT GROUP BY | | 4 | 1 | 3 |00:00:00.01 | 4 | 2048 | 2048 | 2048 (0)|
| 5 | TABLE ACCESS BY INDEX ROWID| EMP | 4 | 5 | 14 |00:00:00.01 | 4 | | | |
|* 6 | INDEX RANGE SCAN | FK_EMP | 4 | 5 | 14 |00:00:00.01 | 2 | | | |
------------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
6 - access("DEPTNO"="D"."DEPTNO")
- Oracle 10g
SQL> SELECT /*+ OPTIMIZER_FEATURES_ENABLE('10.2.0.3') LEADING( D ) USE_NL( E ) NO_MERGE( E ) PUSH_PRED( E ) */ D.DEPTNO, D.DNAME, E.AVG_SAL
2 FROM DEPT D
3 , (SELECT DEPTNO, AVG(SAL) AVG_SAL FROM EMP GROUP BY DEPTNO ) E
4 WHERE E.DEPTNO(+) = D.DEPTNO;
------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |
------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 4 |00:00:00.01 | 13 | | | |
| 1 | NESTED LOOPS OUTER | | 1 | 4 | 4 |00:00:00.01 | 13 | | | |
| 2 | TABLE ACCESS FULL | DEPT | 1 | 4 | 4 |00:00:00.01 | 7 | | | |
|* 3 | VIEW | | 4 | 1 | 3 |00:00:00.01 | 6 | | | |
| 4 | SORT GROUP BY | | 4 | 3 | 12 |00:00:00.01 | 6 | 2048 | 2048 | 2048 (0)|
| 5 | TABLE ACCESS FULL| EMP | 1 | 14 | 14 |00:00:00.01 | 6 | | | |
------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - filter("E"."DEPTNO"="D"."DEPTNO")
- Oracle 10g 스칼라 서브쿼리로 부분범위 처리
SQL> SELECT /*+ OPTIMIZER_FEATURES_ENABLE('10.2.0.3') */D.DEPTNO, D.DNAME
2 , (SELECT AVG(SAL) FROM EMP WHERE DEPTNO = D.DEPTNO) AS AVG_SAL
3 FROM DEPT D;
-------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
-------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 4 |00:00:00.01 | 7 |
| 1 | SORT AGGREGATE | | 4 | 1 | 4 |00:00:00.01 | 4 |
| 2 | TABLE ACCESS BY INDEX ROWID| EMP | 4 | 5 | 14 |00:00:00.01 | 4 |
|* 3 | INDEX RANGE SCAN | FK_EMP | 4 | 5 | 14 |00:00:00.01 | 2 |
| 4 | TABLE ACCESS FULL | DEPT | 1 | 4 | 4 |00:00:00.01 | 7 |
-------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - access("DEPTNO"=:B1)
-- 집계합수가 여러개일때 문제 쿼리
SQL> SELECT /*+ OPTIMIZER_FEATURES_ENABLE('10.2.0.3') */ D.DEPTNO, D.DNAME
2 , (SELECT AVG(SAL) FROM EMP WHERE DEPTNO = D.DEPTNO) AS AVG_SAL
3 , (SELECT MIN(SAL) FROM EMP WHERE DEPTNO = D.DEPTNO) AS AVG_SAL
4 , (SELECT MAX(SAL) FROM EMP WHERE DEPTNO = D.DEPTNO) AS AVG_SAL
5 FROM DEPT D;
-------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
-------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 4 |00:00:00.01 | 7 |
| 1 | SORT AGGREGATE | | 4 | 1 | 4 |00:00:00.01 | 4 |
| 2 | TABLE ACCESS BY INDEX ROWID| EMP | 4 | 5 | 14 |00:00:00.01 | 4 |
|* 3 | INDEX RANGE SCAN | FK_EMP | 4 | 5 | 14 |00:00:00.01 | 2 |
| 4 | SORT AGGREGATE | | 4 | 1 | 4 |00:00:00.01 | 4 |
| 5 | TABLE ACCESS BY INDEX ROWID| EMP | 4 | 5 | 14 |00:00:00.01 | 4 |
|* 6 | INDEX RANGE SCAN | FK_EMP | 4 | 5 | 14 |00:00:00.01 | 2 |
| 7 | SORT AGGREGATE | | 4 | 1 | 4 |00:00:00.01 | 4 |
| 8 | TABLE ACCESS BY INDEX ROWID| EMP | 4 | 5 | 14 |00:00:00.01 | 4 |
|* 9 | INDEX RANGE SCAN | FK_EMP | 4 | 5 | 14 |00:00:00.01 | 2 |
| 10 | TABLE ACCESS FULL | DEPT | 1 | 4 | 4 |00:00:00.01 | 7 |
-------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - access("DEPTNO"=:B1)
6 - access("DEPTNO"=:B1)
9 - access("DEPTNO"=:B1)
-- 위 쿼리 효율적을 Trace 로 확인 가능..
SQL> SELECT /*+ OPTIMIZER_FEATURES_ENABLE('10.2.0.3') */ DEPTNO, DNAME
2 , TO_NUMBER( SUBSTR( SAL, 1, 7 ) ) AVG_SAL
3 , TO_NUMBER( SUBSTR( SAL, 8, 7 ) ) MIN_SAL
4 , TO_NUMBER( SUBSTR( SAL, 15 ) ) MAX_SAL
5 FROM (SELECT /*+ NO_MERGE */ D.DEPTNO, D.DNAME
6 , (SELECT LPAD( AVG(SAL), 7 ) || LPAD(MIN(SAL), 7) || MAX(SAL)
7 FROM EMP WHERE DEPTNO = D.DEPTNO) AS SAL
8 FROM DEPT D
9 ) ;
-------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
-------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 4 |00:00:00.01 | 11 |
| 1 | SORT AGGREGATE | | 4 | 1 | 4 |00:00:00.01 | 4 |
| 2 | TABLE ACCESS BY INDEX ROWID| EMP | 4 | 5 | 14 |00:00:00.01 | 4 |
|* 3 | INDEX RANGE SCAN | FK_EMP | 4 | 5 | 14 |00:00:00.01 | 2 |
| 4 | VIEW | | 1 | 4 | 4 |00:00:00.01 | 11 |
| 5 | TABLE ACCESS FULL | DEPT | 1 | 4 | 4 |00:00:00.01 | 7 |
-------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - access("DEPTNO"=:B1)
5. 조건절 이행
- ( A = B ) 이고 ( B = C ) 이면 (A = C)이다.
-- BATCH I/O
SQL> SELECT *
2 FROM DEPT D
3 , EMP E
4 WHERE E.JOB = 'MANAGER'
5 AND E.DEPTNO = 10
6 AND D.DEPTNO = E.DEPTNO;
-----------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
-----------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 1 |00:00:00.01 | 7 |
| 1 | NESTED LOOPS | | 1 | | 1 |00:00:00.01 | 7 |
| 2 | NESTED LOOPS | | 1 | 1 | 3 |00:00:00.01 | 5 |
| 3 | TABLE ACCESS BY INDEX ROWID| DEPT | 1 | 1 | 1 |00:00:00.01 | 3 |
|* 4 | INDEX RANGE SCAN | DEPT_PK | 1 | 1 | 1 |00:00:00.01 | 2 |
|* 5 | INDEX RANGE SCAN | FK_EMP | 1 | 3 | 3 |00:00:00.01 | 2 |
|* 6 | TABLE ACCESS BY INDEX ROWID | EMP | 3 | 1 | 1 |00:00:00.01 | 2 |
-----------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
4 - access("D"."DEPTNO"=10)
5 - access("E"."DEPTNO"=10)
6 - filter("E"."JOB"='MANAGER')
--
SQL> SELECT /*+ OPTIMIZER_FEATURES_ENABLE('11.2.0.3') NO_NLJ_BATCHING(@SEL$1 E@SEL$1) */ *
2 FROM DEPT D
3 , EMP E
4 WHERE E.JOB = 'MANAGER'
5 AND E.DEPTNO = 10
6 AND D.DEPTNO = E.DEPTNO;
-- AND D.DEPTNO = 10
--------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
--------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 1 |00:00:00.01 | 6 |
| 1 | NESTED LOOPS | | 1 | 1 | 1 |00:00:00.01 | 6 |
| 2 | TABLE ACCESS BY INDEX ROWID| DEPT | 1 | 1 | 1 |00:00:00.01 | 2 |
|* 3 | INDEX UNIQUE SCAN | DEPT_PK | 1 | 1 | 1 |00:00:00.01 | 1 |
|* 4 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 1 | 1 |00:00:00.01 | 4 |
|* 5 | INDEX RANGE SCAN | FK_EMP | 1 | 3 | 3 |00:00:00.01 | 2 |
--------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - access("D"."DEPTNO"=10)
4 - filter("E"."JOB"='MANAGER')
5 - access("E"."DEPTNO"=10)
6. 불필요한 조인 제거
- PK/FK 존재시 조인제거( Join Elimination ) 함
SQL> SELECT E.EMPNO, E.ENAME, E.DEPTNO, E.SAL, E.HIREDATE
2 FROM DEPT D, EMP E
3 WHERE D.DEPTNO = E.DEPTNO;
-------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | Reads |
-------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 14 |00:00:00.04 | 11 | 1 |
| 1 | NESTED LOOPS | | 1 | 14 | 14 |00:00:00.04 | 11 | 1 |
| 2 | TABLE ACCESS FULL| EMP | 1 | 14 | 14 |00:00:00.04 | 7 | 1 |
|* 3 | INDEX UNIQUE SCAN| DEPT_PK | 14 | 1 | 14 |00:00:00.01 | 4 | 0 |
-------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - access("D"."DEPTNO"="E"."DEPTNO")
ALTER TABLE SCOTT.EMP ADD (
CONSTRAINT FK_DEPTNO
FOREIGN KEY (DEPTNO)
REFERENCES SCOTT.DEPT (DEPTNO));
SQL> SELECT E.EMPNO, E.ENAME, E.DEPTNO, E.SAL, E.HIREDATE
2 FROM DEPT D, EMP E
3 WHERE D.DEPTNO = E.DEPTNO;
------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 14 |00:00:00.01 | 4 |
| 1 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 14 | 14 |00:00:00.01 | 4 |
|* 2 | INDEX FULL SCAN | FK_EMP | 1 | 14 | 14 |00:00:00.01 | 2 |
------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter("E"."DEPTNO" IS NOT NULL)
- EMP의 DEPTNO 칼럼이 Null 허용 컬럼이면 결과가 틀리게 될 수 있다. ( null 조인 실패 )
- filter("E"."DEPTNO" IS NOT NULL) <- 옵티마이저
- Outer 10g
SQL> SELECT /*+ OPTIMIZER_FEATURES_ENABLE('10.2.0.3') */ E.EMPNO, E.ENAME, E.DEPTNO, E.SAL, E.HIREDATE
2 FROM DEPT D, EMP E
3 WHERE D.DEPTNO(+) = E.DEPTNO;
----------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
----------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 14 |00:00:00.01 | 11 |
| 1 | NESTED LOOPS OUTER| | 1 | 14 | 14 |00:00:00.01 | 11 |
| 2 | TABLE ACCESS FULL| EMP | 1 | 14 | 14 |00:00:00.01 | 7 |
|* 3 | INDEX UNIQUE SCAN| DEPT_PK | 14 | 1 | 14 |00:00:00.01 | 4 |
----------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - access("D"."DEPTNO"="E"."DEPTNO")
- Outer 11g
SQL> SELECT /*+ OPTIMIZER_FEATURES_ENABLE('11.2.0.3') */ E.EMPNO, E.ENAME, E.DEPTNO, E.SAL, E.HIREDA
2 FROM DEPT D, EMP E
3 WHERE D.DEPTNO(+) = E.DEPTNO;
------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 14 |00:00:00.01 | 7 |
| 1 | TABLE ACCESS FULL| EMP | 1 | 14 | 14 |00:00:00.01 | 7 |
------------------------------------------------------------------------------------
- SQL Server
SELECT E.EMPNO, E.ENAME, E.DEPTNO, E.SAL, E.HIREDA
FROM DOB.DEPT D RIGTH OUTER JOIN DBO.EMP E
ON D.DEPTNO = E.DEPTNO;
EMP 테이블, 스캔 수 1, 논리적 읽기 수 2, 물리적 읽 수 0, 미리 읽기 수 0.
@,.@ ( P.587 )
7. OR 조건을 Union으로 변환
- INDEX COMBINE 으로 풀리수도 있다.
SQL> SELECT *
2 FROM EMP
3 WHERE JOB = 'CLERK' OR DEPTNO = 20;
------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 4 |00:00:00.01 | 7 |
|* 1 | TABLE ACCESS FULL| EMP | 1 | 5 | 4 |00:00:00.01 | 7 |
------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter(("JOB"='CLERK' OR "DEPTNO"=2))
SQL> CREATE INDEX EMP_JOB_IDX ON EMP ( JOB );
인덱스가 생성되었습니다.
SQL> SELECT *
2 FROM EMP
3 WHERE JOB = 'CLERK' OR DEPTNO = 20;
------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 7 |00:00:00.01 | 7 |
|* 1 | TABLE ACCESS FULL| EMP | 1 | 8 | 7 |00:00:00.01 | 7 |
------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter(("DEPTNO"=20 OR "JOB"='CLERK'))
SQL> SELECT /*+ USE_CONCAT */ *
2 FROM EMP
3 WHERE JOB = 'CLERK' OR DEPTNO = 20;
------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 7 |00:00:00.01 | 6 |
| 1 | CONCATENATION | | 1 | | 7 |00:00:00.01 | 6 |
| 2 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 4 | 4 |00:00:00.01 | 4 |
|* 3 | INDEX RANGE SCAN | EMP_JOB_IDX | 1 | 4 | 4 |00:00:00.01 | 2 |
|* 4 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 4 | 3 |00:00:00.01 | 2 |
|* 5 | INDEX RANGE SCAN | FK_EMP | 1 | 5 | 5 |00:00:00.01 | 1 |
------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - access("JOB"='CLERK')
4 - filter(LNNVL("JOB"='CLERK'))
5 - access("DEPTNO"=20)
SQL> SELECT *
2 FROM EMP
3 WHERE JOB = 'CLERK'
4 UNION ALL
5 SELECT *
6 FROM EMP
7 WHERE DEPTNO = 20
8 AND LNNVL( JOB = 'CLERK' );
------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 7 |00:00:00.01 | 6 |
| 1 | UNION-ALL | | 1 | | 7 |00:00:00.01 | 6 |
| 2 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 4 | 4 |00:00:00.01 | 4 |
|* 3 | INDEX RANGE SCAN | EMP_JOB_IDX | 1 | 4 | 4 |00:00:00.01 | 2 |
|* 4 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 4 | 3 |00:00:00.01 | 2 |
|* 5 | INDEX RANGE SCAN | FK_EMP | 1 | 5 | 5 |00:00:00.01 | 1 |
------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - access("JOB"='CLERK')
SQL> SELECT /*+ NO_EXPAND */ *
2 FROM EMP
3 WHERE JOB = 'CLERK' OR DEPTNO = 20;
------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 7 |00:00:00.01 | 7 |
|* 1 | TABLE ACCESS FULL| EMP | 1 | 8 | 7 |00:00:00.01 | 7 |
------------------------------------------------------------------------------------
1 - filter(("DEPTNO"=20 OR "JOB"='CLERK'))
- LNNVL( JOB = 'CLERK' ) : JOB < > 'CLERK' && JOB IS NULL ( 조건식이 false 이거나 Unknown 값일 때 true를 리턴한다.
8. 기타 쿼리 변환
가. 집합연산을 조인으로 변환
- Intersect나 Minus값은 집합(Set) 연산을 조인 형태로 변환하는 것을 말한다.
- 집합 연산
SQL> SELECT JOB, MGR FROM EMP
2 MINUS
3 SELECT JOB, MGR FROM EMP
4 WHERE DEPTNO = 10;
-----------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |
-----------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 5 |00:00:00.01 | 8 | | | |
| 1 | MINUS | | 1 | | 5 |00:00:00.01 | 8 | | | |
| 2 | SORT UNIQUE | | 1 | 14 | 8 |00:00:00.01 | 6 | 2048 | 2048 | 2048 (0)|
| 3 | TABLE ACCESS FULL | EMP | 1 | 14 | 14 |00:00:00.01 | 6 | | | |
| 4 | SORT UNIQUE | | 1 | 3 | 3 |00:00:00.01 | 2 | 2048 | 2048 | 2048 (0)|
| 5 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 3 | 3 |00:00:00.01 | 2 | | | |
|* 6 | INDEX RANGE SCAN | FK_EMP | 1 | 3 | 3 |00:00:00.01 | 1 | | | |
-----------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
6 - access("DEPTNO"=10)
SQL> ;
1 select ksppinm name,
2 ksppstvl value,
3 ksppstdf is_default,
4 decode(bitand(ksppiflg/256,1),1,'true','false') ses_modifiable,
5 decode(bitand(ksppiflg/65536,3),1,'immediate',2,'deferred',3,'immediate','false') sys_modifiable, ksppdesc descrition
6 from sys.x$ksppi i, sys.x$ksppcv v
7 where i.indx = v.indx
8* and i.ksppinm like '%&1%'
SQL> /
Enter value for 1: convert_set_to_join
old 8: and i.ksppinm like '%&1%'
new 8: and i.ksppinm like '%convert_set_to_join%'
NAME VALUE IS_DEFAULT SES_MODIFIABLE SYS_MODIFIABLE DESCRITION
---------------------------------- --------------- --------------- --------------- --------------- ------------------------------
_convert_set_to_join FALSE TRUE true immediate enables conversion of set oper
ator to join
SQL> SELECT /*+ opt_param('_convert_set_to_join','true' ) */ JOB, MGR FROM EMP
2 MINUS
3 SELECT JOB, MGR FROM EMP
4 WHERE DEPTNO = 10;
-----------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |
-----------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 5 |00:00:00.01 | 8 | | | |
| 1 | HASH UNIQUE | | 1 | 6 | 5 |00:00:00.01 | 8 | 1115K| 1115K| 866K (0)|
|* 2 | HASH JOIN ANTI | | 1 | 6 | 9 |00:00:00.01 | 8 | 947K| 947K| 800K (0)|
| 3 | TABLE ACCESS FULL | EMP | 1 | 14 | 14 |00:00:00.01 | 6 | | | |
| 4 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 3 | 3 |00:00:00.01 | 2 | | | |
|* 5 | INDEX RANGE SCAN | FK_EMP | 1 | 3 | 3 |00:00:00.01 | 1 | | | |
-----------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access(SYS_OP_MAP_NONNULL("JOB")=SYS_OP_MAP_NONNULL("JOB") AND
SYS_OP_MAP_NONNULL("MGR")=SYS_OP_MAP_NONNULL("MGR"))
5 - access("DEPTNO"=10)
SQL> SELECT DISTINCT JOB, MGR
2 FROM EMP E
3 WHERE NOT EXISTS(SELECT 'X'
4 FROM EMP
5 WHERE DEPTNO = 10
6 AND SYS_OP_MAP_NONNULL(JOB)=SYS_OP_MAP_NONNULL(E.JOB)
7 AND SYS_OP_MAP_NONNULL(MGR)=SYS_OP_MAP_NONNULL(E.MGR));
-----------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | OMem | 1Mem | Used-Mem |
-----------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 5 |00:00:00.01 | 8 | | | |
| 1 | HASH UNIQUE | | 1 | 6 | 5 |00:00:00.01 | 8 | 1115K| 1115K| 843K (0)|
|* 2 | HASH JOIN ANTI | | 1 | 6 | 9 |00:00:00.01 | 8 | 947K| 947K| 767K (0)|
| 3 | TABLE ACCESS FULL | EMP | 1 | 14 | 14 |00:00:00.01 | 6 | | | |
| 4 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 3 | 3 |00:00:00.01 | 2 | | | |
|* 5 | INDEX RANGE SCAN | FK_EMP | 1 | 3 | 3 |00:00:00.01 | 1 | | | |
-----------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access(SYS_OP_MAP_NONNULL("JOB")=SYS_OP_MAP_NONNULL("E"."JOB") AND
SYS_OP_MAP_NONNULL("MGR")=SYS_OP_MAP_NONNULL("E"."MGR"))
5 - access("DEPTNO"=10)
-- SYS_OP_MAP_NONNULL
SQL> SELECT 1
2 FROM DUAL
3 WHERE NULL = NULL;
선택된 레코드가 없습니다.
SQL> SELECT 1
2 FROM DUAL
3 WHERE SYS_OP_MAP_NONNULL( NULL ) = SYS_OP_MAP_NONNULL( NULL )
4 ;
1
----------
1
조인 칼럼에 IS NOT NULL 조건 추가
- NULL 조인시 실패하기 때문에 필터 조건을 추가하여 불필요한 테이블 엑세스(?) 및 조인 시도를 줄일 수 있어 쿼리 성능 향상에 도움이 된다.
- FTS : Oracle의 경우 null값 비중이 5% 이상일 때) 내부적으로 추가해준다.
- Single Column Index Scan : 싱글 컬럼일때는 널값을 가지고 있지 않기 때문에 조인 칼럼에 IS NOT NULL 조건 추가 불필요..
- Multi Column Index Scan : 글쎄.. 테스트 해봐야할듯 ;;
SQL> SELECT COUNT(*), COUNT(DEPTNO)
2 FROM EMP
3 WHERE SAL <= 2900;
COUNT(*) COUNT(DEPTNO)
---------- -------------
10 10
SQL> INSERT INTO EMP VALUES( 7940, 'MILLER', 'CLERK', '7782', '1982-01-23', 2900, NULL, NULL, NULL );
SQL> SELECT COUNT(*), COUNT(DEPTNO)
2 FROM EMP
3 WHERE SAL <= 2900;
COUNT(*) COUNT(DEPTNO)
---------- -------------
11 10
-- 널값이 5% 이상인 상태에서 컬럼 통계정보가 존재하면 넣어주지만..
SQL> SELECT /*+ LEADING( E ) USE_NL( D ) */ COUNT(E.EMPNO), COUNT(D.DNAME)
2 FROM EMP E, DEPT D
3 WHERE E.DEPTNO = D.DEPTNO
4 AND SAL <= 2900 ;
COUNT(E.EMPNO) COUNT(D.DNAME)
-------------- --------------
10 10
---------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
---------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 1 |00:00:00.01 | 20 |
| 1 | SORT AGGREGATE | | 1 | 1 | 1 |00:00:00.01 | 20 |
| 2 | NESTED LOOPS | | 1 | | 10 |00:00:00.01 | 20 |
| 3 | NESTED LOOPS | | 1 | 10 | 10 |00:00:00.01 | 10 |
|* 4 | TABLE ACCESS FULL | EMP | 1 | 10 | 11 |00:00:00.01 | 6 |
|* 5 | INDEX UNIQUE SCAN | DEPT_PK | 11 | 1 | 10 |00:00:00.01 | 4 |
| 6 | TABLE ACCESS BY INDEX ROWID| DEPT | 10 | 1 | 10 |00:00:00.01 | 10 |
---------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
4 - filter("SAL"<=2900)
5 - access("E"."DEPTNO"="D"."DEPTNO")
SQL> EXEC DBMS_STATS.GATHER_TABLE_STATS( USER, 'EMP', METHOD_OPT=>'FOR ALL COLUMNS', NO_INVALIDATE=>FALSE);
SQL> SELECT /*+ LEADING( E ) USE_NL( D ) */ COUNT(E.EMPNO), COUNT(D.DNAME)
2 FROM EMP E, DEPT D
3 WHERE E.DEPTNO = D.DEPTNO
4 AND SAL <= 2900 ;
COUNT(E.EMPNO) COUNT(D.DNAME)
-------------- --------------
10 10
----------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
----------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 1 |00:00:00.01 | 16 |
| 1 | SORT AGGREGATE | | 1 | 1 | 1 |00:00:00.01 | 16 |
| 2 | NESTED LOOPS | | 1 | | 10 |00:00:00.01 | 16 |
| 3 | NESTED LOOPS | | 1 | 10 | 10 |00:00:00.01 | 6 |
|* 4 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 10 | 10 |00:00:00.01 | 2 |
|* 5 | INDEX FULL SCAN | FK_EMP | 1 | 14 | 14 |00:00:00.01 | 1 |
|* 6 | INDEX UNIQUE SCAN | DEPT_PK | 10 | 1 | 10 |00:00:00.01 | 4 |
| 7 | TABLE ACCESS BY INDEX ROWID | DEPT | 10 | 1 | 10 |00:00:00.01 | 10 |
----------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
4 - filter("SAL"<=2900)
5 - filter("E"."DEPTNO" IS NOT NULL)
6 - access("E"."DEPTNO"="D"."DEPTNO")
27 개의 행이 선택되었습니다.
- no_invalidate == false: 통계 정보 갱신 후 관련된 SQL Cursor들을 즉시 invalidate한다. 9i에서의 기본값이다.
- no_invalidate == true: 통계 정보 갱신 후 관련된 SQL Cursor들을 invalidate하지 않는다. SQL Cursor들이 Shared Pool에서 age-out 된 후 reaload될 때 갱신된 통계 정보가 사용된다.
필터 조건 추가
SQL> SELECT *
2 FROM EMP
3 WHERE SAL BETWEEN 1000 AND 2000;
------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |
------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 6 |00:00:00.01 | 7 |
|* 1 | TABLE ACCESS FULL| EMP | 1 | 6 | 6 |00:00:00.01 | 7 |
------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter(("SAL"<=2000 AND "SAL">=1000))
SQL> SELECT *
2 FROM EMP
3 WHERE SAL BETWEEN 2000 AND 1000
4 ;
---------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 0 |00:00:00.01 |
|* 1 | FILTER | | 1 | | 0 |00:00:00.01 |
|* 2 | TABLE ACCESS FULL| EMP | 0 | 1 | 0 |00:00:00.01 |
---------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter(NULL IS NOT NULL)
2 - filter(("SAL"<=1000 AND "SAL">=2000))
"구루비 데이터베이스 스터디모임" 에서 2013년에 "SQL 전문가 가이드" 도서를 스터디하면서 정리한 내용 입니다.
- 강좌 URL : http://www.gurubee.net/lecture/2401
- 구루비 강좌는 개인의 학습용으로만 사용 할 수 있으며, 다른 웹 페이지에 게재할 경우에는 출처를 꼭 밝혀 주시면 고맙겠습니다.~^^
- 구루비 강좌는 서비스 제공을 위한 목적이나, 학원 홍보, 수익을 얻기 위한 용도로 사용 할 수 없습니다.
) 버튼을 클릭하여 작성 하시면 됩니다.