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nigelbaylissnigelbayliss
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expression stats example (#169)
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‎optimizer/expression_stats/README.md

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

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

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

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