Again I wasn't able to understand this on the docu. I tried this steps:
SQL>exec dbms_stats.gather_table_stats(user, 'EMP', method_opt => 'FOR COLUMNS SIZE 10 empno');
SQL> select endpoint_value ev, endpoint_number en, endpoint_actual_value eav
2 from user_tab_histograms
3 where table_name = 'EMP'
4 and column_name = 'EMPNO'
5 /
EV EN EAV
---------- ---------- --------------------
7369 1
7499 2
7566 3
7654 4
7782 5
7788 6
7844 7
7876 8
7902 9
7934 10
10 rows selected.
Based on the docs the endpoint_number is the bucket, and the endpoint_value is the "normalized" endpoint value. What does it mean by normalized? How does it differ in the endpoint_actual_value column? Here I assume the endpoint_value are the actual values in the empno column, is that right? and from bucket 2 to bucket 3, it means those empno between 7499 and 7566 was within that range. I did a select of empno
SQL> select empno
2 from emp
3 order by empno;
EMPNO
----------
7369
7499
7521
7566
7654
7698
7782
7788
7839
7844
7876
EMPNO
----------
7900
7902
7934
14 rows selected.
Does this mean 7521 is between bucket 2 and 3? Is that how I should interpret it? If so how would I know the exact/estimate number of *values* of empno between those two buckets? for me to know which value (i.e. which empno) appears in many records and which empno appears in one or two rows.
Also if I tried the ename:
SQL> exec dbms_stats.gather_table_stats(user, 'EMP', method_opt => 'FOR COLUMNS SIZE 10 ename');
PL/SQL procedure successfully completed.
SQL> l
1 select endpoint_number en, endpoint_value ev
2 from user_tab_histograms
3 where table_name = 'EMP'
4* and column_name = 'ENAME'
SQL> /
EN EV
---------- ----------
1 3.3888E+35
2 3.3905E+35
3 3.4943E+35
4 3.6507E+35
5 3.8584E+35
6 3.9091E+35
7 4.0129E+35
8 4.3233E+35
9 4.3788E+35
10 4.5305E+35
10 rows selected.
why does the endpoint_value contains numbers and not the values of ename (which I think is because endpoint_value is a number column), but in this case what would my interpretation should be?
Hope I've explained it well. Thank you very much again!
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