by-nc-sa     개발자, DBA가 함께 만들어가는 구루비 지식창고!

6. 스칼라 서브쿼리를 이용한 조인

Added by 이재현, last edited by 이재현 on 9월 01, 2010



06 스칼라 서브쿼리를 이용한 조인

(1) 스칼라 서브쿼리

  • 스칼라 서브쿼리 : 함수처럼 한 레코드당 정확히 하나의 값만을 리턴하는 서브쿼리를 '스칼라 서브쿼리'라고 한다.(select-list)
  • 스칼라 서브쿼리의 테이블은 NL 조인에서 Inner 테이블의 역할을 수행하고 Driving 테이블로부터 조인 조건을 상수로 제공 받는다.
    스칼라 서브 쿼리 
    SQL> select /*+ gather_plan_statistics */ empno, ename, sal, hiredate
  2       , (select d.dname from dept d where d.deptno = e.deptno ) dname
  3   from emp e
  4  where sal >= 2000;
SQL> select * from table( dbms_xplan.display_cursor( null, null, 'ALLSTATS LAST'));
-------------------------------------------------------------------------------------------------
| Id  | Operation                   | Name    | Starts | E-Rows | A-Rows |   A-Time   | Buffers |
-------------------------------------------------------------------------------------------------
|   1 |  TABLE ACCESS BY INDEX ROWID| DEPT    |      3 |      1 |      3 |00:00:00.01 |       5 |

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
|*  2 |   INDEX UNIQUE SCAN         | PK_DEPT |      3 |      1 |      3 |00:00:00.01 |       2 |
|*  3 |  TABLE ACCESS FULL          | EMP     |      1 |     11 |      6 |00:00:00.01 |       8 |
-------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   2 - access("D"."DEPTNO"=:B1)
   3 - filter("SAL">=2000)
    Outer Join 
    select /*+ gather_plan_statistics ordered use_nl(d)*/ 
       e.empno, e.ename, e.sal, e.hiredate, d.dname
  from emp e, dept d
 where d.deptno(+) = e.deptno
   and e.sal >= 2000;
SQL> select * from table( dbms_xplan.display_cursor( null, null, 'ALLSTATS LAST'));
--------------------------------------------------------------------------------------------------
| Id  | Operation                    | Name    | Starts | E-Rows | A-Rows |   A-Time   | Buffers |
--------------------------------------------------------------------------------------------------

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
|   1 |  NESTED LOOPS OUTER          |         |      1 |     11 |      6 |00:00:00.01 |      16 |
|*  2 |   TABLE ACCESS FULL          | EMP     |      1 |     11 |      6 |00:00:00.01 |       8 |
|   3 |   TABLE ACCESS BY INDEX ROWID| DEPT    |      6 |      1 |      6 |00:00:00.01 |       8 |
|*  4 |    INDEX UNIQUE SCAN         | PK_DEPT |      6 |      1 |      6 |00:00:00.01 |       2 |
--------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   2 - filter("E"."SAL">=2000)
   4 - access("D"."DEPTNO"="E"."DEPTNO")
  • 위에서 예시한 쿼리는 결과만 같은 것이 아니라 조인을 수행하는 처리 경로도 동일한데, NL 방식으로 수행되도록 힌트를 사용했기 때문임

(2) 스칼라 서브쿼리의 캐싱 효과

  • 오라클은 스칼라 서브 쿼리 수행 회수를 최소화 하려고 그 입력 값과 출력 값을 내부 캐시(Query Execution Cache)에 저장해 둔다.
  • 스칼라 서브쿼리가 수행될 때면 일단 '입력 값'을 캐시에서 찾아 보고 거기 있으면 저장된 '출력 값'을 리턴한다.
  • 캐시에서 찾지 못할 때만 쿼리를 수행하며, 결과는 버리지 않고 캐시에 저장해둔다.
    스칼라 서브 쿼리 케시 알고리즘 
    select empno, ename, sal, hiredate
     , (select d.dname              -> 출력값 : d.dname
          from dept d
	 where d.deptno = e.empno   -> 입력값 : e.empno
       )
  from emp e
 where sal >= 2000
    TEST 준비 스크립트 
    SQL> CREATE TABLE T_CODE AS
  2  SELECT ROWNUM CODE, CHR(ROWNUM + 64) NAME FROM DUAL
  3  CONNECT BY LEVEL <= 1000

SQL> CREATE INDEX IDX_T_CODE_PK ON T_CODE(CODE,NAME);

SQL> ALTER TABLE T_CODE ADD CONSTRAINT IDX_T_CODE_PK PRIMARY KEY(CODE);

SQL> CREATE TABLE T AS
  2  SELECT ROWNUM NO, CEIL(ROWNUM/1000) CODE  FROM DUAL
  3  CONNECT BY LEVEL <= 1000000;

SQL> CREATE INDEX IDX_T_01 ON T( CODE);

SQL> EXEC DBMS_STATS.GATHER_TABLE_STATS(USER, 'T');

SQL> EXEC DBMS_STATS.GATHER_TABLE_STATS(USER, 'T_CODE');

CREATE or REPLACE FUNCTION GET_NAME(IN_CODE INT)
RETURN VARCHAR
IS
RET_NAME T_CODE.NAME%TYPE;
BEGIN
  SELECT NAME 
    INTO RET_NAME
    FROM T_CODE WHERE CODE = IN_CODE;
  RETURN RET_NAME;
END;
/
    일반 펑션 
    SQL> SELECT /*+ gather_plan_statistics*/COUNT(T)
  2    FROM (
  3  SELECT GET_NAME(CODE) AS T
  4    FROM T)
  5    ;

  COUNT(T)
----------
   1000000

SQL> select * from table( dbms_xplan.display_cursor( null, null, 'ALLSTATS LAST'));

-------------------------------------------------------------------------------------
| Id  | Operation          | Name | Starts | E-Rows | A-Rows |   A-Time   | Buffers |
-------------------------------------------------------------------------------------
|   1 |  SORT AGGREGATE    |      |      1 |      1 |      1 |00:00:17.42 |    2003K|

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
|   2 |   TABLE ACCESS FULL| T    |      1 |    994K|   1000K|00:00:00.01 |    1925 |
-------------------------------------------------------------------------------------
    스칼라 서브 쿼리 사용한 펑션 
    SQL> SELECT /*+ gather_plan_statistics*/COUNT(T) 
  2    FROM (                                    
  3  SELECT (SELECT GET_NAME(CODE) FROM DUAL) AS T                  
  4    FROM T)                                   
  5    ;                                         

  COUNT(T)
----------
   1000000

SQL> select * from table( dbms_xplan.display_cursor( null, null, 'ALLSTATS LAST'));

-------------------------------------------------------------------------------------
| Id  | Operation          | Name | Starts | E-Rows | A-Rows |   A-Time   | Buffers |
-------------------------------------------------------------------------------------
|   1 |  FAST DUAL         |      |   1000 |      1 |   1000 |00:00:00.01 |       0 |

PLAN_TABLE_OUTPUT
---------------------------------------------------------------------------------------------------
|   2 |  SORT AGGREGATE    |      |      1 |      1 |      1 |00:00:00.18 |    3927 |
|   3 |   TABLE ACCESS FULL| T    |      1 |    994K|   1000K|00:00:00.01 |    1925 |
-------------------------------------------------------------------------------------

|
  • 입력값과 출력 값을 빠르게 저장하고 찾기 위해 오라클은 해싱 알고리즘을 사용한다.
  • '비용기반의 오라클 원리'저자 조나단 루이스 설명에 의하면 8i, 9i에서는 256개 엔트리를 캐싱하고
  • 10에서는 입력과 출력값 크기,_query_execution_cach_max_size파라미터에 의해 캐시 사이즈가 결정된다고 한다.
  • 해시 충돌이 발생했을 때 기존 엔트리를 밀어내고 새로 수행한 입력 값과 출력 값으로 대체할 것 같지만,
    오라클은 기존 캐시 엔트리를 그대로 둔 채 스칼라 서브 쿼리만 한 번 더 수행하고 만다.따라서 해시 충돌이 발생한 입력 값이 반복적으로
    입력되면 스칼라 서브쿼리도 반복 수행된다.
    결론 : 스칼라 서브쿼리의 캐싱 효과는 입력 값의 종류가 소수여서 해시 충돌 가능성이 적은 때라야 효과가 있으며
    , 반대의 경우라며 캐시를 확인하는 비용 때문에 오히려 성능은 저하되고 CPU 사용률만 높게 만든다.
    게다가 스칼라 서브쿼리를 사용하면 NL조인에서 Inner 쪽인덱스와 테이블에 나타나는 버퍼 Pinning 효과도 사라진다는 사실을 기억할 필요가 있다.

(3) 두 개 이상의 값을 리턴하고 싶을 때

'CHICAGO'인 부서만 대상으로 급여 수준을 집계하려는 것인데, 사원 테이블 전체를 다 읽어야 하는 비효율 발생이라는데...(어라 변형이..._) 
SQL> select /*+gather_plan_statistics*/d.deptno, d.dname, avg_sal, min_sal, max_sal
  2  from   dept d                                                                             
  3       ,(select deptno, avg(sal) avg_sal, min(sal) min_sal, max(sal) max_sal                
  4         from emp group by deptno) e                                                        
  5  where  e.deptno(+) = d.deptno                                                             
  6  and    d.loc = 'CHICAGO';                                                                 

    DEPTNO DNAME             AVG_SAL    MIN_SAL    MAX_SAL
---------- -------------- ---------- ---------- ----------
        30 SALES          1566.66667        950       2850

SQL> select * from table( dbms_xplan.display_cursor( null, null, 'ALLSTATS LAST'));

----------------------------------------------------------------------------------------------------
| Id  | Operation                     | Name    | Starts | E-Rows | A-Rows |   A-Time   | Buffers |  OMem |  1Mem | Us
----------------------------------------------------------------------------------------------------

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
|   1 |  HASH GROUP BY                |         |      1 |      1 |      1 |00:00:00.01 |       3 |       |       |          |
|   2 |   MERGE JOIN OUTER            |         |      1 |      5 |      6 |00:00:00.01 |       3 |       |       |          |
|*  3 |    TABLE ACCESS BY INDEX ROWID| DEPT    |      1 |      1 |      1 |00:00:00.01 |       2 |       |       |          |
|   4 |     INDEX FULL SCAN           | PK_DEPT |      1 |      4 |      4 |00:00:00.01 |       1 |       |       |          |
|*  5 |    SORT JOIN                  |         |      1 |     14 |      6 |00:00:00.01 |       1 |  2048 |  2048 | 2048  (0)|
|   6 |     INDEX FULL SCAN           | EMP_X01 |      1 |     14 |     14 |00:00:00.01 |       1 |       |       |          |
----------------------------------------------------------------------------------------------------

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
   3 - filter("D"."LOC"='CHICAGO')
   5 - access("DEPTNO"="D"."DEPTNO")
       filter("DEPTNO"="D"."DEPTNO")
(잠시 딴애기)위 쿼리가 변형 일어나 아래처럼 됨.. 비효율 발생이 없는듯.. 근데 왜 머지로 풀리지.?? 할것없다구했는데.. ㅠ 
SQL> SELECT /*+gather_plan_statistics */D.deptno, D.DNAME, avg(sal) avg_sal, min(sal) min_sal, max(sal) max_sal  
  2    FROM EMP E
  3       , DEPT D
  4   WHERE E.DEPTNO(+) = D.DEPTNO
  5     AND D.LOC = 'CHICAGO'
  6   GROUP BY D.deptno, D.DNAME;

    DEPTNO DNAME             AVG_SAL    MIN_SAL    MAX_SAL
---------- -------------- ---------- ---------- ----------
        30 SALES          1566.66667        950       2850

SQL> select * from table( dbms_xplan.display_cursor( null, null, 'ALLSTATS LAST'));

----------------------------------------------------------------------------------------------------
| Id  | Operation                     | Name    | Starts | E-Rows | A-Rows |   A-Time   | Buffers |  OMem |  1Mem | Us
----------------------------------------------------------------------------------------------------
|   1 |  HASH GROUP BY                |         |      1 |      1 |      1 |00:00:00.01 |       3 |       |       |          |

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
|   2 |   MERGE JOIN OUTER            |         |      1 |      5 |      6 |00:00:00.01 |       3 |       |       |          |
|*  3 |    TABLE ACCESS BY INDEX ROWID| DEPT    |      1 |      1 |      1 |00:00:00.01 |       2 |       |       |          |
|   4 |     INDEX FULL SCAN           | PK_DEPT |      1 |      4 |      4 |00:00:00.01 |       1 |       |       |          |
|*  5 |    SORT JOIN                  |         |      1 |     14 |      6 |00:00:00.01 |       1 |  2048 |  2048 | 2048  (0)|
|   6 |     INDEX FULL SCAN           | EMP_X01 |      1 |     14 |     14 |00:00:00.01 |       1 |       |       |          |
----------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   3 - filter("D"."LOC"='CHICAGO')

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
   5 - access("E"."DEPTNO"="D"."DEPTNO")
       filter("E"."DEPTNO"="D"."DEPTNO")

|
(잠시 딴애기)NO_MERGE 1 
SQL> select /*+gather_plan_statistics LEADING(E) INDEX(E PK_EMP) USE_HASH(E) NO_MERGE(E)*/
  2        d.deptno, d.dname, avg_sal, min_sal, max_sal                                             
                                    
  3  from   dept d                                                                                  
                                                                                             
  4       ,(select deptno, avg(sal) avg_sal, min(sal) min_sal, max(sal) max_sal     
  5         from emp group by deptno) e                                             
  6  where  e.deptno(+) = d.deptno                                                  
  7  and    d.loc = 'CHICAGO';                                                      

    DEPTNO DNAME             AVG_SAL    MIN_SAL    MAX_SAL
---------- -------------- ---------- ---------- ----------
        30 SALES          1566.66667        950       2850

SQL>  select * from table( dbms_xplan.display_cursor( null, null, 'ALLSTATS LAST'));

----------------------------------------------------------------------------------------------------
| Id  | Operation                      | Name   | Starts | E-Rows | A-Rows |   A-Time   | Buffers |  OMem |  1Mem | U
----------------------------------------------------------------------------------------------------

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
|*  1 |  HASH JOIN OUTER               |        |      1 |      1 |      1 |00:00:00.01 |       9 |   921K|   921K|  291K (0)|
|*  2 |   TABLE ACCESS FULL            | DEPT   |      1 |      1 |      1 |00:00:00.01 |       7 |       |       |          |
|   3 |   VIEW                         |        |      1 |      3 |      3 |00:00:00.01 |       2 |       |       |          |
|   4 |    HASH GROUP BY               |        |      1 |      3 |      3 |00:00:00.01 |       2 |       |       |          |
|   5 |     TABLE ACCESS BY INDEX ROWID| EMP    |      1 |     14 |     14 |00:00:00.01 |       2 |       |       |          
|   6 |      INDEX FULL SCAN           | PK_EMP |      1 |     14 |     14 |00:00:00.01 |       1 |       |       |          
----------------------------------------------------------------------------------------------------

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
   1 - access("E"."DEPTNO"="D"."DEPTNO")
   2 - filter("D"."LOC"='CHICAGO')
|
(잠시 딴애기)NO_MERGE 2 
SQL> select /*+gather_plan_statistics no_merge(e)*/d.deptno, d.dname, avg_sal, min_sal, max_sal  
  2  from   dept d                                                                   
  3       ,(select deptno, avg(sal) avg_sal, min(sal) min_sal, max(sal) max_sal      
  4         from emp group by deptno) e                                              
  5  where  e.deptno(+) = d.deptno                                                   
  6  and    d.loc = 'CHICAGO';   

    DEPTNO DNAME             AVG_SAL    MIN_SAL    MAX_SAL
---------- -------------- ---------- ---------- ----------
        30 SALES          1566.66667        950       2850

SQL> select * from table( dbms_xplan.display_cursor( null, null, 'ALLSTATS LAST'));

----------------------------------------------------------------------------------------------------
| Id  | Operation                    | Name    | Starts | E-Rows | A-Rows |   A-Time   | Buffers |  OMem |  1Mem 
----------------------------------------------------------------------------------------------------

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
|   1 |  MERGE JOIN OUTER            |         |      1 |      1 |      1 |00:00:00.08 |      11 |       |       |          |
|*  2 |   TABLE ACCESS BY INDEX ROWID| DEPT    |      1 |      1 |      1 |00:00:00.04 |       4 |       |       |      
|   3 |    INDEX FULL SCAN           | PK_DEPT |      1 |      4 |      4 |00:00:00.03 |       2 |       |       |          |
|*  4 |   SORT JOIN                  |         |      1 |      3 |      1 |00:00:00.04 |       7 |  2048 |  2048 | 20
|   5 |    VIEW                      |         |      1 |      3 |      3 |00:00:00.04 |       7 |       |       |          |
|   6 |     HASH GROUP BY            |         |      1 |      3 |      3 |00:00:00.04 |       7 |       |       |          |
|   7 |      TABLE ACCESS FULL       | EMP     |      1 |     14 |     14 |00:00:00.02 |       7 |       |
----------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------

   2 - filter("D"."LOC"='CHICAGO')
   4 - access("E"."DEPTNO"="D"."DEPTNO")
       filter("E"."DEPTNO"="D"."DEPTNO")
|
스칼라 서브 쿼리는 한 레코드당 하나의 값만 리턴함(아래 쿼리 불가능(X)) 
select d.deptno, d.dname
     ,(select avg(sal), min(sal), max(sal) from emp where deptno = d.deptno)
from   dept d 
where  d.loc = 'CHICAGO';
|
반복적 수행 (비효율) 
SQL> select /*+gather_plan_statistics*/d.deptno, d.dname
  2       ,(select avg(sal) from emp where deptno = d.deptno) avg_sal
  3       ,(select min(sal) from emp where deptno = d.deptno) min_sal
  4       ,(select max(sal) from emp where deptno = d.deptno) max_sal
  5  from   dept d 
  6  where  d.loc = 'CHICAGO';

    DEPTNO DNAME             AVG_SAL    MIN_SAL    MAX_SAL
---------- -------------- ---------- ---------- ----------
        30 SALES          1566.66667        950       2850

SQL> select * from table( dbms_xplan.display_cursor( null, null, 'ALLSTATS LAST'));

---------------------------------------------------------------------------------------
| Id  | Operation         | Name    | Starts | E-Rows | A-Rows |   A-Time   | Buffers |

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
---------------------------------------------------------------------------------------
|   1 |  SORT AGGREGATE   |         |      1 |      1 |      1 |00:00:00.01 |       1 |
|*  2 |   INDEX RANGE SCAN| EMP_X01 |      1 |      5 |      6 |00:00:00.01 |       1 |
|   3 |  SORT AGGREGATE   |         |      1 |      1 |      1 |00:00:00.01 |       1 |
|*  4 |   INDEX RANGE SCAN| EMP_X01 |      1 |      5 |      6 |00:00:00.01 |       1 |
|   5 |  SORT AGGREGATE   |         |      1 |      1 |      1 |00:00:00.01 |       1 |
|*  6 |   INDEX RANGE SCAN| EMP_X01 |      1 |      5 |      6 |00:00:00.01 |       1 |
|*  7 |  TABLE ACCESS FULL| DEPT    |      1 |      1 |      1 |00:00:00.01 |       8 |
---------------------------------------------------------------------------------------

Predicate Information (identified by operation id):

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
---------------------------------------------------

   2 - access("DEPTNO"=:B1)
   4 - access("DEPTNO"=:B1)
   6 - access("DEPTNO"=:B1)
   7 - filter("D"."LOC"='CHICAGO')
|
substr함수 사용(오~ XPLAN 두 되는군요 =_=) 
SQL> SELECT /*+ GATHER_PLAN_STATISTICS */
  2         DEPTNO
  3       , DNAME
  4       , TO_NUMBER(SUBSTR(SAL, 1, 7)) AVG_SAL
  5       , TO_NUMBER(SUBSTR(SAL, 8, 7)) MIN_SAL
  6       , TO_NUMBER(SUBSTR(SAL, 15)) MAX_SAL
  7    FROM (SELECT D.DEPTNO, D.DNAME
  8        , (SELECT LPAD(AVG(SAL), 7)||LPAD(MIN(SAL),7)||MAX(SAL)
  9      FROM EMP
 10     WHERE DEPTNO = D.DEPTNO) SAL
 11     FROM DEPT D
 12    WHERE D.LOC = 'CHICAGO'
 13  )
 14  ;

    DEPTNO DNAME             AVG_SAL    MIN_SAL    MAX_SAL
---------- -------------- ---------- ---------- ----------
        30 SALES             1566.66        950       2850

SQL> select * from table( dbms_xplan.display_cursor( null, null, 'ALLSTATS LAST'));

---------------------------------------------------------------------------------------

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
| Id  | Operation         | Name    | Starts | E-Rows | A-Rows |   A-Time   | Buffers |
---------------------------------------------------------------------------------------
|   1 |  SORT AGGREGATE   |         |      1 |      1 |      1 |00:00:00.01 |       1 |
|*  2 |   INDEX RANGE SCAN| EMP_X01 |      1 |      5 |      6 |00:00:00.01 |       1 |
|*  3 |  TABLE ACCESS FULL| DEPT    |      1 |      1 |      1 |00:00:00.01 |       8 |
---------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   2 - access("DEPTNO"=:B1)

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
   3 - filter("D"."LOC"='CHICAGO')
|
오브젝트 TYPE을 사용하는 방식 
SQL>  CREATE OR REPLACE TYPE SAL_TYPE AS OBJECT
  2  (AVG_SAL NUMBER, MIN_SAL NUMBER, MAX_SAL NUMBER)
  3  /

유형이 생성되었습니다.

SQL> SELECT /*+ GATHER_PLAN_STATISTICS */DEPTNO, DNAME
  2       , A.SAL.AVG_SAL, A.SAL.MIN_SAL, A.SAL.MAX_SAL
  3    FROM (SELECT D.DEPTNO, D.DNAME
  4               , (SELECT SAL_TYPE(AVG(SAL), MIN(SAL), MAX(SAL) )
  5                    FROM EMP WHERE DEPTNO = D.DEPTNO) SAL
  6            FROM DEPT D WHERE D.LOC = 'CHICAGO')A
  7   ;

    DEPTNO DNAME          SAL.AVG_SAL SAL.MIN_SAL SAL.MAX_SAL
---------- -------------- ----------- ----------- -----------
        30 SALES           1566.66667         950        2850

SQL> select * from table( dbms_xplan.display_cursor( null, null, 'ALLSTATS LAST'));

---------------------------------------------------------------------------------------
| Id  | Operation         | Name    | Starts | E-Rows | A-Rows |   A-Time   | Buffers |

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
---------------------------------------------------------------------------------------
|   1 |  SORT AGGREGATE   |         |      1 |      1 |      1 |00:00:00.01 |       1 |
|*  2 |   INDEX RANGE SCAN| EMP_X01 |      1 |      5 |      6 |00:00:00.01 |       1 |
|*  3 |  TABLE ACCESS FULL| DEPT    |      1 |      1 |      1 |00:00:00.01 |       8 |
---------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   2 - access("DEPTNO"=:B1)
   3 - filter("D"."LOC"='CHICAGO')
|

문서정보

Enter labels to add to this page:
Please wait 
Looking for a label? Just start typing.