Height Balanced类型的直方图
SQL> execute dbms_stats.gather_table_stats(ownname=>'SCOTT',tabname=>'H',estimate_percent => 100,method_opt => 'for columns size 1 x',cascade=>true);
PL/SQL 过程已成功完成。
查询：
SQL> select table_name,column_name,num_distinct,num_buckets,histogram from user_tab_col_statistics where table_name='H';
TABLE_NAME COLUMN_NAM NUM_DISTINCT NUM_BUCKETS HISTOGRAM
------------------------------ ---------- ------------ ----------- ---------------
H X 10 1 NONE
SQL> select table_name,column_name,endpoint_number,endpoint_value from user_tab_histograms where table_name='H';
TABLE_NAME COLUMN_NAM ENDPOINT_NUMBER ENDPOINT_VALUE
------------------------------ ---------- --------------- --------------
H X 0 1
H X 1 49
SQL> execute dbms_stats.gather_table_stats(ownname=>'SCOTT',tabname=>'H',estimate_percent => 100,method_opt => 'for columns size 5 x',cascade=>true);
PL/SQL 过程已成功完成。
查询为高度直方图：
SQL> select table_name,column_name,num_distinct,density,num_buckets,histogram from user_tab_col_statistics where table_name='H';
TABLE_NAME COLUMN_NAM NUM_DISTINCT DENSITY NUM_BUCKETS HISTOGRAM
------------------------------ ---------- ------------ ---------- ----------- ---------------
H X 10 .085276318 5 HEIGHT BALANCED
SQL> select table_name,column_name,endpoint_number,endpoint_value from user_tab_histograms where table_name='H' order by endpoint_value;
TABLE_NAME COLUMN_NAM ENDPOINT_NUMBER ENDPOINT_VALUE
------------------------------ ---------- --------------- --------------
H X 0 1
H X 1 7
H X 3 10
H X 4 32
H X 5 49
SQL> execute dbms_stats.gather_table_stats(ownname=>'SCOTT',tabname=>'H',estimate_percent => 100,method_opt => 'for columns size 1 x',cascade=>true);
PL/SQL 过程已成功完成。
查询：
SQL> select table_name,column_name,num_distinct,num_buckets,histogram from user_tab_col_statistics where table_name='H';
TABLE_NAME COLUMN_NAM NUM_DISTINCT NUM_BUCKETS HISTOGRAM
------------------------------ ---------- ------------ ----------- ---------------
H X 10 1 NONE
SQL> select table_name,column_name,endpoint_number,endpoint_value from user_tab_histograms where table_name='H';
TABLE_NAME COLUMN_NAM ENDPOINT_NUMBER ENDPOINT_VALUE
------------------------------ ---------- --------------- --------------
H X 0 1
H X 1 49
SQL> execute dbms_stats.gather_table_stats(ownname=>'SCOTT',tabname=>'H',estimate_percent => 100,method_opt => 'for columns size 5 x',cascade=>true);
PL/SQL 过程已成功完成。
查询为高度直方图：
SQL> select table_name,column_name,num_distinct,density,num_buckets,histogram from user_tab_col_statistics where table_name='H';
TABLE_NAME COLUMN_NAM NUM_DISTINCT DENSITY NUM_BUCKETS HISTOGRAM
------------------------------ ---------- ------------ ---------- ----------- ---------------
H X 10 .085276318 5 HEIGHT BALANCED
SQL> select table_name,column_name,endpoint_number,endpoint_value from user_tab_histograms where table_name='H' order by endpoint_value;
TABLE_NAME COLUMN_NAM ENDPOINT_NUMBER ENDPOINT_VALUE
------------------------------ ---------- --------------- --------------
H X 0 1
H X 1 7
H X 3 10
H X 4 32
H X 5 49
来自 “ ITPUB博客 ” ，链接：https://blog.itpub.net/31397003/viewspace-2140253/ ，如需转载，请注明出处，否则将追究法律责任。
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