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