• 휴리스틱 기반의 쿼리 변환 : 특정 조건을 충족시키는 경우 적용
• 비용 기반의 쿼리 변환 : 비용 추정기가 산출한 비용에 근거하여, 원래 실행 계획보다 더 낮은 비용의 실행 계획이 생성될 경우 적용

쿼리 변환 - DISTINCT 추가 (비용 기반)

---------------------
QUERY BLOCK SIGNATURE
---------------------
  signature (): qb_name=SEL$08FE944A nbfros=2 flg=0
    fro(0): flg=0 objn=148792 hint_alias="T1"@"SEL$1"
    fro(1): flg=1 objn=0 hint_alias="VW_DTP_AE9E49E8"@"SEL$AE9E49E8"

DP: Transformed query
******* UNPARSED QUERY IS *******
SELECT DISTINCT "T1"."N2" "N2","VW_DTP_AE9E49E8"."ITEM_2" "N2" FROM  (SELECT DISTINCT "T2"."T1_ID" "ITEM_1","T2"."N2" "ITEM_2" FROM "CHRIS"."T2" "T2") "VW_DTP_AE9E49E8","CHRIS"."T1" "T1" WHERE "T1"."ID"="VW_DTP_AE9E49E8"."ITEM_1"
FPD: Considering simple filter push in query block SEL$08FE944A (#1)
"T1"."ID"="VW_DTP_AE9E49E8"."ITEM_1"
try to generate transitive predicate from check constraints for query block SEL$08FE944A (#1)
finally: "T1"."ID"="VW_DTP_AE9E49E8"."ITEM_1"

FPD: Considering simple filter push in query block SEL$BCD4421C (#2)
 ??
OJE: Begin: find best directive for query block SEL$BCD4421C (#2)
OJE: End: finding best directive for query block SEL$BCD4421C (#2)
DP: Costing query block.
CBQT: Looking for cost annotations for query block SEL$BCD4421C, key = SEL$BCD4421C_00001000_2
CBQT: Could not find stored cost annotations.
kkoqbc: optimizing query block SEL$BCD4421C (#2)

        :
    call(in-use=16704, alloc=65656), compile(in-use=186616, alloc=190344), execution(in-use=218808, alloc=220376)

kkoqbc-subheap (create addr=0x7ff50b393ed0)

(중간 생략)

****************
QUERY BLOCK TEXT
****************
SELECT DISTINCT t1.n2, t2.n2 FROM t1, t2 WHERE t1.id = t2.t1_id


SELECT DISTINCT "T1"."N2" "N2",
       "VW_DTP_AE9E49E8"."ITEM_2" "N2"
  FROM (SELECT DISTINCT "T2"."T1_ID" "ITEM_1",
               "T2"."N2" "ITEM_2"
          FROM "CHRIS"."T2" "T2") "VW_DTP_AE9E49E8",
       "CHRIS"."T1" "T1"
 WHERE "T1"."ID"="VW_DTP_AE9E49E8"."ITEM_1"