小编hak*_*aki的帖子

这是场景

SQL> exec dbms_stats.gather_table_stats(user,'TM', cascade=>true)

PL/SQL procedure successfully completed.

SQL> SELECT SEGMENT_NAME , SEGMENT_TYPE , BYTES / 1024 / 1024 MB , BLOCKS FROM DBA_SEGMENTS WHERE SEGMENT_NAME IN ('TM', 'TM_LD_IX');

SEGMENT_NAME            SEGMENT_TYPE        MB        BLOCKS
------------------------------------------ ---------- ----------
TM                      TABLE                 296      37888
TM_LD_IX                INDEX                  46       5888

SQL> select index_name , column_name from user_ind_columns where index_name = 'TM_LD_IX';

INDEX_NAME   COLUMN_NAME
------------ ------------------------------
TM_LD_IX     LD

SQL> explain plan for select distinct LD from TM;

Explained.

SQL> @ex

PLAN_TABLE_OUTPUT
---------------------------------------------------------------------------------------------------------------------------------

Plan hash value: 4241255022 …