搜集直方图repeat和skewonly

SQL> set linesize 200
SQL>   select a.column_name,
                   b.num_rows,
                  a.num_distinct Cardinality,
                    round(a.num_distinct / b.num_rows * 100, 2) selectivity,
                   a.histogram,
                  a.num_buckets
              from dba_tab_col_statistics a, dba_tables b
             where a.owner = b.owner
              and a.table_name = b.table_name
            and a.owner = 'MBFE'
         and a.table_name = upper('messagein');  2    3    4    5    6    7    8    9   10   11  

COLUMN_NAME			 NUM_ROWS CARDINALITY SELECTIVITY HISTOGRAM	  NUM_BUCKETS
------------------------------ ---------- ----------- ----------- --------------- -----------
ID				   978619      978619	      100 NONE			    1
MSGID				   978619      978619	      100 FREQUENCY		    2
STATUS				   978619	    1		0 NONE			    1
PROCCNT 			   978619	    2		0 NONE			    1
ACCEPTTIME			   978619      653888	    66.82 NONE			    1
MSGBODY 			   978619	    0		0 NONE			    0
QUEUE				   978619	    4		0 NONE			    1

7 rows selected.



SQL>  BEGIN
          DBMS_STATS.GATHER_TABLE_STATS(ownname          => 'MBFE',
                                       tabname          => 'MESSAGEIN',
                                      estimate_percent => 100,
                                        method_opt       => 'for columns MSGID size 1',
                                      no_invalidate    => FALSE,
                                       degree           => 16,
                                       cascade          => TRUE);
       END;  2    3    4    5    6    7    8    9  
 10  /

PL/SQL procedure successfully completed.


SQL>   select a.column_name,
                   b.num_rows,
                  a.num_distinct Cardinality,
                    round(a.num_distinct / b.num_rows * 100, 2) selectivity,
                   a.histogram,
                  a.num_buckets
              from dba_tab_col_statistics a, dba_tables b
             where a.owner = b.owner
              and a.table_name = b.table_name
            and a.owner = 'MBFE'
         and a.table_name = upper('messagein');  2    3    4    5    6    7    8    9   10   11  

COLUMN_NAME			 NUM_ROWS CARDINALITY SELECTIVITY HISTOGRAM	  NUM_BUCKETS
------------------------------ ---------- ----------- ----------- --------------- -----------
ID				   978619      978619	      100 NONE			    1
MSGID				   978619      978619	      100 NONE			    1
STATUS				   978619	    1		0 NONE			    1
PROCCNT 			   978619	    2		0 NONE			    1
ACCEPTTIME			   978619      653888	    66.82 NONE			    1
MSGBODY 			   978619	    0		0 NONE			    0
QUEUE				   978619	    4		0 NONE			    1

7 rows selected.

此时直方图已经被干掉

SQL>  BEGIN
          DBMS_STATS.GATHER_TABLE_STATS(ownname          => 'MBFE',
                                       tabname          => 'MESSAGEIN',
                                      estimate_percent => 100,
                                        method_opt       => 'for columns MSGID size repeat',
                                      no_invalidate    => FALSE,
                                       degree           => 16,
                                       cascade          => TRUE);
       END;  2    3    4    5    6    7    8    9  
 10  /

PL/SQL procedure successfully completed.

SQL> ^C^C

SQL> 
SQL> select a.column_name,
                   b.num_rows,
                  a.num_distinct Cardinality,
                    round(a.num_distinct / b.num_rows * 100, 2) selectivity,
                   a.histogram,
                  a.num_buckets
              from dba_tab_col_statistics a, dba_tables b
             where a.owner = b.owner
              and a.table_name = b.table_name
            and a.owner = 'MBFE'
         and a.table_name = upper('messagein');  2    3    4    5    6    7    8    9   10   11  

COLUMN_NAME			 NUM_ROWS CARDINALITY SELECTIVITY HISTOGRAM	  NUM_BUCKETS
------------------------------ ---------- ----------- ----------- --------------- -----------
ID				   978619      978619	      100 NONE			    1
MSGID				   978619      978619	      100 NONE			    1
STATUS				   978619	    1		0 NONE			    1
PROCCNT 			   978619	    2		0 NONE			    1
ACCEPTTIME			   978619      653888	    66.82 NONE			    1
MSGBODY 			   978619	    0		0 NONE			    0
QUEUE				   978619	    4		0 NONE			    1

7 rows selected.

SQL> 

用repert 方式收集：
repeat表示以前收集过直方图，现在收集统计信息的时候就收集直方图，如果以前没收集过直方图，现在收集统计信息的时候就不收集。

此时无效果
SQL> BEGIN
          DBMS_STATS.GATHER_TABLE_STATS(ownname          => 'MBFE',
                                       tabname          => 'MESSAGEIN',
                                      estimate_percent => 100,
                                        method_opt       => 'for columns MSGID size skewonly',
                                      no_invalidate    => FALSE,
                                       degree           => 16,
                                       cascade          => TRUE);
       END;  2    3    4    5    6    7    8    9  
 10  /

PL/SQL procedure successfully completed.

SQL> select a.column_name,
       b.num_rows,
       a.num_distinct Cardinality,
       round(a.num_distinct / b.num_rows * 100, 2) selectivity,
       a.histogram,
       a.num_buckets
  from dba_tab_col_statistics a, dba_tables b
 where a.owner = b.owner
   and a.table_name = b.table_name
   and a.owner = 'MBFE'
   and a.table_name = upper('messagein');
  2    3    4    5    6    7    8    9   10   11  
COLUMN_NAME			 NUM_ROWS CARDINALITY SELECTIVITY HISTOGRAM	  NUM_BUCKETS
------------------------------ ---------- ----------- ----------- --------------- -----------
ID				   978619      978619	      100 NONE			    1
MSGID				   978619      978619	      100 FREQUENCY		    2
STATUS				   978619	    1		0 NONE			    1
PROCCNT 			   978619	    2		0 NONE			    1
ACCEPTTIME			   978619      653888	    66.82 NONE			    1
MSGBODY 			   978619	    0		0 NONE			    0
QUEUE				   978619	    4		0 NONE			    1

7 rows selected.

此时已搜集：

skewonly 对所有的列搜集统计信息