• 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 - GROUP-BY 추가 (비용 기반)

---------------------
QUERY BLOCK SIGNATURE
---------------------
  signature (): qb_name=SEL$1928AB68 nbfros=2 flg=0
    fro(0): flg=0 objn=148796 hint_alias="T1"@"SEL$1"
    fro(1): flg=1 objn=0 hint_alias="VW_GBF_1"@"SEL$AE9E49E8"

GBP: Transformed query
******* UNPARSED QUERY IS *******
SELECT "T1"."N2" "N2","VW_GBF_1"."ITEM_3" "N2",SUM("VW_GBF_1"."ITEM_2") "COUNT(*)" FROM  (SELECT "T2"."T1_ID" "ITEM_1",COUNT(*) "ITEM_2","T2"."N2" "ITEM_3" FROM "CHRIS"."T2" "T2" GROUP BY "T2"."T1_ID","T2"."N2") "VW_GBF_1","CHRIS"."T1" "T1" WHERE "T1"."ID"="VW_GBF_1"."ITEM_1" GROUP BY "T1"."N2","VW_GBF_1"."ITEM_3"
  Column (#2): T1_ID(
    AvgLen: 3 NDV: 100 Nulls: 0 Density: 0.010000 Min: 1 Max: 100
  Column (#4): N2(
    AvgLen: 4 NDV: 4200 Nulls: 0 Density: 0.000238 Min: 0 Max: 4199
FPD: Considering simple filter push in query block SEL$1928AB68 (#1)
"T1"."ID"="VW_GBF_1"."ITEM_1"
try to generate transitive predicate from check constraints for query block SEL$1928AB68 (#1)
finally: "T1"."ID"="VW_GBF_1"."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$BCD4421C (#2)
GBP: Costing transformed query.
CBQT: Looking for cost annotations for query block SEL$BCD4421C, key = SEL$BCD4421C_00001000_2
CBQT: Could not find stored cost annotations.
kkoqbc: optimizing query block SEL$BCD4421C (#2)

        :
    call(in-use=18544, alloc=65656), compile(in-use=197384, alloc=214536), execution(in-use=245240, alloc=248864)

kkoqbc-subheap (create addr=0x7f0ec118fb58)

(중간 생략)

****************
QUERY BLOCK TEXT
****************
SELECT t1.n2, t2.n2, count(*) FROM t1, t2 WHERE t1.id = t2.t1_id GROUP BY t1.n2, t2.n2


SELECT "T1"."N2" "N2",
       "VW_GBF_1"."ITEM_3" "N2",
       SUM("VW_GBF_1"."ITEM_2") "COUNT(*)"
  FROM (SELECT "T2"."T1_ID" "ITEM_1",
               COUNT(*) "ITEM_2",
               "T2"."N2" "ITEM_3"
          FROM "CHRIS"."T2" "T2"
         GROUP BY "T2"."T1_ID",
               "T2"."N2") "VW_GBF_1",
       "CHRIS"."T1" "T1"
 WHERE "T1"."ID"="VW_GBF_1"."ITEM_1"
 GROUP BY "T1"."N2",
       "VW_GBF_1"."ITEM_3"