收集统计信息

我们使用method_opt => 'for all columns size auto'方式对表收集统计信息。

SQL> BEGIN
      DBMS_STATS.GATHER_TABLE_STATS(ownname          => 'SCOTT',
                                    tabname          => 'T_STATS',
                                    estimate_percent => 100,
                                    method_opt       => 'for all columns size auto',
                                    no_invalidate    => FALSE,
                                    degree           => 1,
                                    cascade          => TRUE);
    END

我们查看直方图信息。

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

COLUMN_NAME       NUM_ROWS  NUM_NULLS CARDINALITY SELECTIVITY HISTOGRAM   NUM_BUCKETS
--------------- ---------- ---------- ----------- ----------- --------------- -------
EDITION_NAME         72674      72674           0           0 NONE                  0
NAMESPACE            72674          1          21         .03 NONE                  1
SECONDARY            72674          0           2           0 NONE                  1
GENERATED            72674          0           2           0 NONE                  1
TEMPORARY            72674          0           2           0 NONE                  1
STATUS               72674          0           2           0 NONE                  1
TIMESTAMP            72674          1        1592        2.19 NONE                  1
LAST_DDL_TIME        72674          1        1521        2.09 NONE                  1
CREATED              72674          0        1472        2.03 NONE                  1
OBJECT_TYPE          72674          0          45         .06 NONE                  1
DATA_OBJECT_ID       72674      64833        7796       10.73 NONE                  1
OBJECT_ID            72674          1       72673         100 NONE                  1
SUBOBJECT_NAME       72674      72145         140         .19 NONE                  1
OBJECT_NAME          72674          0       44333          61 NONE                  1
OWNER                72674          0          31         .04 FREQUENCY            31

15 rows selected.