expression stats example

optimizer/expression_stats/README.md

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+Small demo to show how expression statistics can improve cardinality estimates
+
+# Disclaimer
+
+ <br/>-- These scripts are provided for educational purposes only.
+ <br/>-- They are NOT supported by Oracle World Wide Technical Support.
+ <br/>-- The scripts have been tested and they appear to work as intended.
+ <br/>-- You should always run scripts on a test instance.
+
+

optimizer/expression_stats/expression.lst

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+
+Table created.
+
+
+ COUNT(*)
+----------
+ 1773
+
+
+PL/SQL procedure successfully completed.
+
+
+ COUNT(*)
+----------
+ 1773
+
+
+PLAN_TABLE_OUTPUT
+----------------------------------------------------------------------------------------------------
+SQL_ID 8caz15dwj8w8k, child number 0
+-------------------------------------
+SELECT /* MYQUERY */ COUNT(*) FROM t WHERE ( "DELIVERY_DATE" >=
+trunc(sysdate@!, 'fmyear') AND ( coalesce("CONTROL_FLAG", 1) = 1
+OR coalesce("CONTROL_FLAG", 1) = 3 ) AND (
+coalesce(substr(to_char("ACCOUNT_ID"), 4, 1), '1') = '1' OR
+coalesce(substr(to_char("ACCOUNT_ID"), 4, 1), '1') = '3' ) AND
+"DELIVERY_DATE" <= trunc(sysdate@! - 1) )
+
+Plan hash value: 1010173228
+
+
+PLAN_TABLE_OUTPUT
+----------------------------------------------------------------------------------------------------
+----------------------------------------------------------------------------
+| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
+----------------------------------------------------------------------------
+| 0 | SELECT STATEMENT | | | | 9 (100)| |
+| 1 | SORT AGGREGATE | | 1 | 15 | | |
+|* 2 | FILTER | | | | | |
+|* 3 | TABLE ACCESS FULL| T | 2 | 30 | 9 (0)| 00:00:01 |
+----------------------------------------------------------------------------
+
+Predicate Information (identified by operation id):
+---------------------------------------------------
+
+PLAN_TABLE_OUTPUT
+----------------------------------------------------------------------------------------------------
+
+ 2 - filter(TRUNC(SYSDATE@!-1)>=TRUNC(SYSDATE@!,'fmyear'))
+ 3 - filter(((COALESCE("CONTROL_FLAG",1)=1 OR
+ COALESCE("CONTROL_FLAG",1)=3) AND "DELIVERY_DATE"<=TRUNC(SYSDATE@!-1)
+ AND (COALESCE(SUBSTR(TO_CHAR("ACCOUNT_ID"),4,1),'1')='1' OR
+ COALESCE(SUBSTR(TO_CHAR("ACCOUNT_ID"),4,1),'1')='3') AND
+ "DELIVERY_DATE">=TRUNC(SYSDATE@!,'fmyear')))
+
+
+30 rows selected.
+
+
+TABLE_NAME OWNER EXPRESSION_TEXT
+---------------------------------------- ---------------------------------------- ----------------------------------------------------------------------------------------------------
+T ADHOC COALESCE(SUBSTR(TO_CHAR("ACCOUNT_ID"),4,1),'1')
+T ADHOC "DELIVERY_DATE"
+T ADHOC COALESCE("CONTROL_FLAG",1)
+
+
+DBMS_STATS.CREATE_EXTENDED_STATS(USER,'T',Q'[(COALESCE("CONTROL_FLAG",1))]')
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+SYS_STUARLGZBSAG4YYL$Q$14300KT
+
+
+DBMS_STATS.CREATE_EXTENDED_STATS(USER,'T',Q'[(COALESCE(SUBSTR(TO_CHAR("ACCOUNT_ID"),4,1),'1'))]')
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+SYS_STU2K568KT2T5R6S37VQUN63#V
+
+
+PL/SQL procedure successfully completed.
+
+
+ COUNT(*)
+----------
+ 1773
+
+
+PLAN_TABLE_OUTPUT
+----------------------------------------------------------------------------------------------------
+SQL_ID 8caz15dwj8w8k, child number 0
+-------------------------------------
+SELECT /* MYQUERY */ COUNT(*) FROM t WHERE ( "DELIVERY_DATE" >=
+trunc(sysdate@!, 'fmyear') AND ( coalesce("CONTROL_FLAG", 1) = 1
+OR coalesce("CONTROL_FLAG", 1) = 3 ) AND (
+coalesce(substr(to_char("ACCOUNT_ID"), 4, 1), '1') = '1' OR
+coalesce(substr(to_char("ACCOUNT_ID"), 4, 1), '1') = '3' ) AND
+"DELIVERY_DATE" <= trunc(sysdate@! - 1) )
+
+Plan hash value: 1010173228
+
+
+PLAN_TABLE_OUTPUT
+----------------------------------------------------------------------------------------------------
+----------------------------------------------------------------------------
+| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
+----------------------------------------------------------------------------
+| 0 | SELECT STATEMENT | | | | 10 (100)| |
+| 1 | SORT AGGREGATE | | 1 | 13 | | |
+|* 2 | FILTER | | | | | |
+|* 3 | TABLE ACCESS FULL| T | 1363 | 17719 | 10 (10)| 00:00:01 |
+----------------------------------------------------------------------------
+
+Predicate Information (identified by operation id):
+---------------------------------------------------
+
+PLAN_TABLE_OUTPUT
+----------------------------------------------------------------------------------------------------
+
+ 2 - filter(TRUNC(SYSDATE@!-1)>=TRUNC(SYSDATE@!,'fmyear'))
+ 3 - filter(("DELIVERY_DATE"<=TRUNC(SYSDATE@!-1) AND
+ COALESCE(SUBSTR(TO_CHAR("ACCOUNT_ID"),4,1),'1') AND
+ "DELIVERY_DATE">=TRUNC(SYSDATE@!,'fmyear') AND
+ COALESCE("CONTROL_FLAG",1)))
+
+
+29 rows selected.
+

optimizer/expression_stats/expression.sql

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+spool expression
+--
+-- Demonstrates the usefulness of expression statistics
+-- Creates a table "T" - and note that session requires
+-- read access to V$SESSION
+--
+set linesize 250
+set trims on
+set tab off
+column plan_table_output format a100
+column expression_text format a100
+column table_name format a40
+column owner format a40
+
+var sqlid varchar2(20)
+
+create table t as
+select sysdate-50+rownum/100 delivery_date,1 control_flag,
+ rownum account_id
+from dual connect by rownum<=10000;
+
+SELECT /* MYQUERY */ COUNT(*)
+FROM t
+WHERE ( "DELIVERY_DATE" >= trunc(sysdate@!, 'fmyear')
+ AND ( coalesce("CONTROL_FLAG", 1) = 1
+ OR coalesce("CONTROL_FLAG", 1) = 3 )
+ AND ( coalesce(substr(to_char("ACCOUNT_ID"), 4, 1), '1') = '1'
+ OR coalesce(substr(to_char("ACCOUNT_ID"), 4, 1), '1') = '3' )
+ AND "DELIVERY_DATE" <= trunc(sysdate@! - 1) );
+
+exec select prev_sql_id into :sqlid from v$session where sid=sys_context('userenv','sid');
+
+SELECT /* MYQUERY */ COUNT(*)
+FROM t
+WHERE ( "DELIVERY_DATE" >= trunc(sysdate@!, 'fmyear')
+ AND ( coalesce("CONTROL_FLAG", 1) = 1
+ OR coalesce("CONTROL_FLAG", 1) = 3 )
+ AND ( coalesce(substr(to_char("ACCOUNT_ID"), 4, 1), '1') = '1'
+ OR coalesce(substr(to_char("ACCOUNT_ID"), 4, 1), '1') = '3' )
+ AND "DELIVERY_DATE" <= trunc(sysdate@! - 1) );
+
+--
+-- Note the poor cardinality estimate of "2"
+--
+SELECT * FROM table(DBMS_XPLAN.DISPLAY_CURSOR());
+
+select distinct table_name,owner,expression_text 
+from dba_expression_statistics 
+where (table_name,owner) 
+ in (select object_name, object_owner 
+ from v$sql_plan 
+ where object_type = 'TABLE' 
+ and sql_id = :sqlid);
+--
+-- Create the expression statistics
+--
+select dbms_stats.create_extended_stats(USER,'T',
+ q'[(COALESCE("CONTROL_FLAG",1))]')
+from dual;
+
+select dbms_stats.create_extended_stats(USER,'T',
+ q'[(COALESCE(SUBSTR(TO_CHAR("ACCOUNT_ID"),4,1),'1'))]') 
+from dual;
+
+begin
+ dbms_stats.gather_table_stats(USER,'T', 
+ method_opt=>q'[for columns (COALESCE("CONTROL_FLAG",1))]', 
+ no_invalidate=>FALSE);
+
+ dbms_stats.gather_table_stats(USER,'T',
+ method_opt=>q'[for columns (COALESCE(SUBSTR(TO_CHAR("ACCOUNT_ID"),4,1),'1'))]',
+ no_invalidate=>FALSE);
+end;
+/
+
+SELECT /* MYQUERY */ COUNT(*)
+FROM t
+WHERE ( "DELIVERY_DATE" >= trunc(sysdate@!, 'fmyear')
+ AND ( coalesce("CONTROL_FLAG", 1) = 1
+ OR coalesce("CONTROL_FLAG", 1) = 3 )
+ AND ( coalesce(substr(to_char("ACCOUNT_ID"), 4, 1), '1') = '1'
+ OR coalesce(substr(to_char("ACCOUNT_ID"), 4, 1), '1') = '3' )
+ AND "DELIVERY_DATE" <= trunc(sysdate@! - 1) );
+
+--
+-- Note the improved cardinality estimate
+--
+SELECT * FROM table(DBMS_XPLAN.DISPLAY_CURSOR());
+
+spool off