1. MERGE 구문으로 처리되는 데이터 이해하기

테스트환경

 

-- [MERGE_T1 TERGET 테이블 생성]
create table merge_t1
    as
select level as c1, chr(65+mod(level,26)) as c2, level+99999 as c3
  from DUAL
connect by level <= 100000 ;

-- [MERGE_T1 인덱스 생성]
create index merge_t1_idx_01 on merge_t1 ( c1 ) ;

-- [MERGE_T1 통계정보 수집]
exec dbms_stats.gather_table_stats(ownname=>'SCOTT',tabname=>'merge_t1',cascade=>TRUE,estimate_percent=>100) ;

-- [MERGE_T2 SOURCE 테이블 생성]
create table merge_t2
as
select level as c1, chr(65+mod(level,26)) as c2,
decode(mod(level,10),0,null,mod(level,10)) as c3
from DUAL
connect by level <= 500000 ;

-- [MERGE_T2 인덱스 생성]
create index merge_t2_idx_01 on merge_t2 ( c1 ) ;

-- [MERGE_T2 통계정보 수집]
exec dbms_stats.gather_table_stats(ownname=>'SCOTT',tabname=>'merge_t2',cascade=>TRUE,estimate_percent=>100) ;

테스트 구문

 
MERGE INTO merge_t1 tt 
USING (
       SELECT c1, c2, c3
         FROM  MERGE_T2
       WHERE c1 >= 99990
          AND c1 <= 100090
        ) st
ON (tt.c1 = st.c1)
WHEN MATCHED THEN
    UPDATE SET tt.c2 = st.c2, ttC3 = st.c3
    DELETE WHERE (tt.c2 = 'A' )
WHERE NOT MATCHED THEN 
    INSERT (tt.C1, tt.c2, tt.c3) VALUES (st.c1, st.c2, st.c3) 
     WHERE (st.c2 = 'A');

1)MERGE_T1 테이블에 몇건이 UPDATE 될까?

 
SELECT COUNT(*)
  FROM (SELECT c1, c2, c3 
         FROM MERGE_T2
        WHERE c1 >= 99990
          AND c1 <= 100090
        )st, MERGE_T1 tt
WHERE st.c1 = tt.c1;

COUNT(*)
--------
      11  <-- 총 11건이  UPDATE 대상임

WHEN MATCHED THEN 데이터

• 총 11건의 MATCHED 데이터중 10건이 UPDATE 되고 1건이 DELETE 됨.

2)MERGE_T1 테이블에 몇건이 DELETE 될까?

 
SELECT COUNT(*)
 FROM MERGE_T1
WHERE c1 >= 99990
  AND c1 <= 100000
  AND c2 = 'A'; ---> MERGE 구문의 DELETE 시 체크 조건

COUNT(*)
--------
      1  <-- 총 1건이  DELETE 대상임.  DELETE 조건과 MATCHED DATA (MERGE_T1.C1 = 99996)

3)MERGE_T1 테이블에 몇건이 INSERT 될까?

 

SELECT c1,c2
 FROM  MERGE_T2
WHERE c1 >= 99990
  AND c1 <= 100090
  and  C2='A'
  minus
SELECT c1,c2
 FROM  MERGE_T1
WHERE c1 >= 99990
  AND c1 <= 100090;

C1     C2
------ ---
100022	A
100048	A
100074	A   <-- 총 3건이 INSERT 대상임