oracle 為什麼沒有使用索引的一種情況

存在以下索引

SQL> SELECT INDEX_NAME,COLUMN_NAME FROM USER_IND_COLUMNS WHERE INDEX_NAME='IDX_GBDS_CLIENT_GAME_EVENT';
 
INDEX_NAME                     COLUMN_NAME
------------------------------ --------------------------------------------------------------------------------
IDX_GBDS_CLIENT_GAME_EVENT     CLIENT_ID
IDX_GBDS_CLIENT_GAME_EVENT     GAME_CODE_ID
IDX_GBDS_CLIENT_GAME_EVENT     EVENT_DATE
IDX_GBDS_CLIENT_GAME_EVENT     BET_TYPE

1.下面這樣寫不會用上索引

SQL> select * from tb_game_bet_detail_snapshot where game_code_id=50000;

no rows selected

Execution Plan
----------------------------------------------------------
   0      SELECT STATEMENT ptimizer=CHOOSE (Cost=7 Card=1050 Bytes=68
          250)

   1    0   TABLE ACCESS (FULL) OF 'TB_GAME_BET_DETAIL_SNAPSHOT' (Cost
          =7 Card=1050 Bytes=68250)

 

 

Statistics
----------------------------------------------------------
          0  recursive calls
          0  db block gets
        126  consistent gets
          0  physical reads
          0  redo size
        778  bytes sent via SQL*Net to client
        364  bytes received via SQL*Net from client
          1  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          0  rows processed

2.把謂詞全部寫上 用上快速索引掃描 一致性讀也降下來

SQL> select client_id,game_code_id,event_date,bet_type from tb_game_bet_detail_s
napshot where game_code_id=50000;

no rows selected

Execution Plan
----------------------------------------------------------
   0      SELECT STATEMENT ptimizer=CHOOSE (Cost=5 Card=1050 Bytes=23
          100)

   1    0   INDEX (FAST FULL SCAN) OF 'IDX_GBDS_CLIENT_GAME_EVENT' (UN
          IQUE) (Cost=5 Card=1050 Bytes=23100)

 

 

Statistics
----------------------------------------------------------
          0  recursive calls
          0  db block gets
         35  consistent gets
          0  physical reads
          0  redo size
        353  bytes sent via SQL*Net to client
        364  bytes received via SQL*Net from client
          1  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          0  rows processed

SQL>