GROUP BY / DISTINCT 跳跃式去重扫描场景问题排查

obclient> select dbms_xplan.display_cursor(0,'all')\G;
*************************** 1. row ***************************
dbms_xplan.display_cursor(0,'all'): ================================================================================================================================================
|ID|OPERATOR         |NAME                                              |EST.ROWS|EST.TIME(us)|REAL.ROWS|REAL.TIME(us)|IO TIME(us)|CPU TIME(us)|
------------------------------------------------------------------------------------------------------------------------------------------------
|0 |MERGE DISTINCT   |                                                  |120     |365475      |54       |804492       |0          |698457      |
|1 |└─TABLE FULL SCAN|tbl_x1(idx_tbl_x1_5)                              |21653574|106216      |21653574 |804492       |0          |105363      |
================================================================================================================================================
is_index_back=false, is_global_index=false, range(MIN,MIN,MIN ; MAX,MAX,MAX)always true

Used Hint:
-------------------------------------
  tbl_x1:
      table_rows:21190271
      physical_range_rows:21653574
      logical_range_rows:21653574
      output_rows:21653574
      table_dop:1

SELECT c11 AS label, c16 AS sonLabel
FROM tbl_x1
GROUP BY c11, c16;

CREATE TABLE `tbl_x1` (
  `c01` char(32) NOT NULL,
  `c02` char(32) NOT NULL,
  `c03` varchar(20) DEFAULT NULL,
  `c04` varchar(20) DEFAULT NULL,
  `c05` varchar(11) DEFAULT NULL,
  `c06` varchar(11) DEFAULT NULL,
  `c07` timestamp(3) NULL DEFAULT NULL,
  `c08` timestamp(3) NULL DEFAULT NULL,
  `c09` char(8) DEFAULT NULL,
  `c10` tinyint(4) DEFAULT NULL,
  `c11` char(2) DEFAULT NULL,
  `c12` varchar(64) DEFAULT NULL,
  `c13` mediumtext DEFAULT NULL,
  `c14` varchar(256) DEFAULT NULL,
  `c15` varchar(60) DEFAULT NULL,
  `c16` varchar(6) DEFAULT NULL,
  `c17` mediumtext DEFAULT NULL,
  `c18` char(32) DEFAULT NULL,
  `c19` timestamp(3) NULL DEFAULT CURRENT_TIMESTAMP(3) ON UPDATE CURRENT_TIMESTAMP(3),
  `c20` char(32) DEFAULT NULL,
  `c21` timestamp(3) NULL DEFAULT CURRENT_TIMESTAMP(3),
  `c22` tinyint(4) DEFAULT '0',
  `c23` char(32) DEFAULT NULL,
  `c24` tinyint(4) DEFAULT NULL,
  `c25` mediumtext DEFAULT NULL,
  `c26` varchar(45) DEFAULT NULL,
  `c27` varchar(45) DEFAULT NULL,
  `c28` char(32) DEFAULT NULL,
  `c29` int(11) DEFAULT '0',
  PRIMARY KEY (`c01`),
  KEY `idx_tbl_x1_1` (`c02`, `c12`) BLOCK_SIZE 16384 LOCAL,
  KEY `idx_tbl_x1_2` (`c28`) BLOCK_SIZE 16384 LOCAL,
  KEY `idx_tbl_x1_4` (`c21`, `c05`, `c28`) BLOCK_SIZE 16384 LOCAL,
  KEY `idx_tbl_x1_5` (`c11`, `c16`) BLOCK_SIZE 16384 LOCAL,
  KEY `idx_tbl_x1_6` (`c14`, `c22`) BLOCK_SIZE 16384 LOCAL,
  KEY `idx_tbl_x1_7` (`c26`) BLOCK_SIZE 16384 LOCAL
) ORGANIZATION INDEX DEFAULT CHARSET=utf8mb4 ROW_FORMAT=DYNAMIC
  COMPRESSION='zstd_1.3.8' REPLICA_NUM=2 BLOCK_SIZE=16384
  USE_BLOOM_FILTER=FALSE ENABLE_MACRO_BLOCK_BLOOM_FILTER=FALSE
  TABLET_SIZE=134217728 PCTFREE=0;

SELECT DISTINCT c11 AS label, c16 AS sonLabel
FROM tbl_x1;