2026-03-12 21:01:38

histograms/histogram_06.txt

@@ -0,0 +1,97 @@
+https://hourim.wordpress.com/?s=histogram
+
+https://jonathanlewis.wordpress.com/2013/10/09/12c-histograms-pt-3/
+
+exec dbms_stats.delete_table_stats('SYS','T1');
+
+
+exec dbms_stats.gather_table_stats(user,'T1', method_opt=>'for columns size 20 col1');
+
+exec dbms_stats.gather_table_stats(user,'T1', method_opt=>'for all columns size 1');
+
+
+
+select
+        endpoint_number,
+        endpoint_value,
+        endpoint_repeat_count
+from
+        user_tab_histograms
+where
+        table_name = 'T1'
+order by
+        endpoint_number
+;
+
+
+set pages 50 lines 256
+
+alter system flush shared_pool;
+
+drop table Q purge;
+
+create table Q as
+   select /*+ GATHER_PLAN_STATISTICS */
+       a.COL1    COL1
+   from
+       T1 a,
+       T1 b
+   where
+     a.COL1=b.COL1
+   /
+
+select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST  +PEEKED_BINDS +PARALLEL +PARTITION +COST +BYTES'));
+
+
+set pages 50 lines 256
+
+alter system flush shared_pool;
+
+drop table Q purge;
+
+create table Q as
+   select /*+ GATHER_PLAN_STATISTICS */
+       a.COL1    COL1
+   from
+       T1 a,
+       T1 b
+   where
+     a.COL1=33 and
+     a.COL1=b.COL1
+   /
+
+select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST  +PEEKED_BINDS +PARALLEL +PARTITION +COST +BYTES'));
+
+
+
+
+set pages 50 lines 256
+
+alter system flush shared_pool;
+
+drop table Q purge;
+
+create table Q as
+   select /*+ GATHER_PLAN_STATISTICS */
+       a.COL1    COL1
+   from
+       T1 a,
+       T1 b
+   where
+     a.COL1=37 and
+     a.COL1=b.COL1
+   /
+
+select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST  +PEEKED_BINDS +PARALLEL +PARTITION +COST +BYTES'));
+
+
+
+37 distinct values - 20 popular values = 17 non popular values
+On 32 lines => 17 non popular values (oniform distributed) => 2 lines / value
+
+
+
+x    17      
+
+
+