Table not using index

15 pts.
Oracle development
Good day, I have a table containing 4 billion records and adding 7 million records per day, working with a date and timestamp. Currently the table is created with a date (charging_date) and a timestamp (named timestamp but with format varchar2(6) - i.e. '065000' for 06H50 AM). I created a new column DATE_TIME where I concatenated the charging_date and timestamp values into a DATE_TIME value with format 'dd-mon-rrrr hh24miss'. However the values stored in this column are store as "1/1/2005 12:06:50 AM" for example. I did create an index on this value and analyzed the table afterwards. When I do a select with a parameter value like the following: select charging_date, timestamp, date_time from cdrdata_new_temp where to_timestamp(date_time,'dd-mon-rrrr hh24miss') = to_timestamp('&from_date','dd-mon-rrrr hh24miss') it is doing a full table scan and don't return any records. It takes about 15 minutes to return after the select. How can I force the select to use the index and what format must the user enter to pick up the value in the DATE_TIME column. The exercise is needed in order to improve the poor performance of the queries on the table. All the queries work on a selection of charging_date and timestamp values. Currently I must concatenate the charging_date and timestamp values in order the get the data in the correct start and end date time combination. This takes forever to return my results. Kind regards Bonita Graupe

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You get no index usage because you indexed a column but you are querying it via an expression.
To enable the usage of an index you must not use the index expression (here: the column) in an expression.

From the way your query is written I assume the type of the new date_time column is VARCHAR2 (otherwise you wouldn’t convert it, I guess).

The best solution would be to store the date_time column either as DATE or TIMESTAMP (not VARCHAR2). Then index the column and if you have all that, rewrite your query to use the column directly:
WHERE date_time = TO_TIMESTAMP(‘&from_date’,’dd-mon-rrrr hh24miss’)


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  • Ascdba
    Just to add to what was said -- Oracle won't use an index on an indexed column if you apply a function to that indexed column in an expression. However, if you must do this (use a function on an indexed field) you should look into Oracle's function-based index -- you create an index based on the use of a function. hth, Andy
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