2026-03-12 21:01:38

histograms/histogram_01.txt

@@ -0,0 +1,86 @@
+# Tracking column histogram modifications by M.Houri
+# https://hourim.wordpress.com/2020/08/06/historical-column-histogram/
+
+
+create table T1 tablespace TS1 as  
+select rownum id, decode(mod(rownum,10),0,2,1) c_freq, nvl(blocks,999) c_hb  
+from dba_tables ; 
+
+update T1 set c_freq=3 where rownum<=10; 
+commit; 
+
+create index idx_freq on T1(C_FREQ) tablespace TS1; 
+create index idx_hb on T1(C_HB) tablespace TS1; 
+
+
+select c_freq,count(*) from T1 group by c_freq order by 2 desc; 
+
+
+exec dbms_stats.gather_table_stats (user, 'T1', method_opt=>'for all columns size 1'); 
+
+col column_name for a20
+
+select column_name,num_distinct,density,num_nulls,num_buckets,sample_size,histogram  
+from user_tab_col_statistics  
+where table_name='T1' and column_name='C_FREQ'; 
+
+
+
+select  /*+ GATHER_PLAN_STATISTICS */ * from T1 where C_FREQ=3; 
+
+select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST  +PEEKED_BINDS +PARALLEL +PARTITION +COST +BYTES'));
+
+
+select column_name,num_distinct,density,num_nulls,num_buckets,sample_size,histogram  
+from user_tab_col_statistics  
+where table_name='T1' and column_name='C_HB'; 
+
+select /*+ GATHER_PLAN_STATISTICS */ * from T1 where C_HB=999; 
+select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST  +PEEKED_BINDS +PARALLEL +PARTITION +COST +BYTES'));
+
+
+---------------- FREQ
+
+exec dbms_stats.gather_table_stats(user,'T1', method_opt=>'for columns C_FREQ size AUTO');
+
+select column_name,num_distinct,density,num_nulls,num_buckets,sample_size,histogram  
+from user_tab_col_statistics  
+where table_name='T1' and column_name='C_FREQ'; 
+
+select endpoint_value as column_value, 
+endpoint_number as cummulative_frequency, 
+endpoint_number - lag(endpoint_number,1,0) over (order by endpoint_number) as frequency 
+from user_tab_histograms 
+where table_name = 'T1' and column_name = 'C_FREQ'; 
+
+alter system flush shared_pool;
+
+select  /*+ GATHER_PLAN_STATISTICS */ * from T1 where C_FREQ=3; 
+
+select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST  +PEEKED_BINDS +PARALLEL +PARTITION +COST +BYTES'));
+
+
+--------------- WEIGHT
+
+exec dbms_stats.gather_table_stats(user,'T1', method_opt=>'for columns C_HB size 254');
+
+select column_name,num_distinct,density,num_nulls,num_buckets,sample_size,histogram  
+from user_tab_col_statistics  
+where table_name='T1' and column_name='C_HB'; 
+
+
+select endpoint_value as column_value, 
+endpoint_number as cummulative_frequency, 
+endpoint_number - lag(endpoint_number,1,0) over (order by endpoint_number) as frequency 
+from user_tab_histograms 
+where table_name = 'T1' and column_name = 'C_HB'; 
+
+
+
+create table T1 tablespace TS1 as  
+select rownum id, decode(mod(rownum,10),0,2,1) c_freq, nvl(blocks,999) c_hb  
+from dba_extents ; 
+
+update T1 set c_freq=3 where rownum<=10; 
+commit; 
+