Question

I have the following sql being run on an Oracle 10g database:

select  /*+ ALL_ROWS */
       to_number(cv.old_value) as cv_id,
       to_number(job.old_value) as job_id
  from amendments,
       amnddets cv,
       amnddets job
 where amendments.table_name = 'TIMESHEET_LAYER'
   and amendments.dml_type = 'D'
   and cv.amnd_id = amendments.amnd_id 
   and cv.column_name = 'CV_ID'
   and job.amnd_id = amendments.amnd_id
   and job.column_name = 'JOB_ID';

There are the following indexes that have been created:

create index amendments_dmp_type_upper on amendments upper(dmp_type);
create index amendments_table_name_upper on amendments upper(table_name);
create index amendments_pk on amendments (amnd_id);
create index amended_column_name_idx on amnddets (column_name);
create index amnddets_amnd_id_idx on amnddets (amnd_id);

I have also tried using ANSI joins (the below sql) but this does not use the indexes either, placing upper() around the table_name and dml_type also has no affect.

The above query is taking approximately 30 – 40 secs to retrieve around 2500 rows.

I looked at the explain plan and can’t see that the index on amendments for table_name and dml_type are being used.

Below is the ANSI explain plan for:

select  /*+ ALL_ROWS */
       to_number(cv.old_value) as cv_id,
       to_number(job.old_value) as job_id
  from amendments
  JOIN amnddets cv on cv.amnd_id = amendments.amnd_id and cv.column_name = 'CV_ID'
  JOIN amnddets job on job.amnd_id = amendments.amnd_id and job.column_name = 'JOB_ID'
 where upper(amendments.table_name) = 'TIMESHEET_LAYER'
   and amendments.dml_type = 'D';

Could any one advise why the table_name, dml_type and column_name indexes aren’t being used in the above query?

Answer 1

If you have actually run this as you say:

create index amendments_dmp_type_upper on amendments upper(dmp_type);

then what you have actually created is an index on amendments(dmp_type) without the upper function!

The correct syntax is:

create index amendments_dmp_type_upper on amendments (upper(dmp_type));

Perhaps surprisingly, your statement works but the word “upper” is treated as a table alias – this works too:

create index amendments_dmp_type_upper on amendments foo(dmp_type);