Simple query with date type requires explicit conversion to_date of date

oracleoracle-11g-r2

My question is, I have a table which contains a column called myDateColumn (for example) which is of the type date:

I can confirm desc myTable contains this line:

myDateColumn  NOT NULL     DATE

However, when I try to select all the data that is between certain dates, for example:

select * from myTable 
where myDateColumn 
between to_date('13-FEB-11', 'DD-MON-YY') AND TO_DATE('15-FEB-11', 'DD-MON-YY');

I get null results no matter what, even though I am sure some data exists within this specific date range.

The fix for it I discovered was to explicitly convert myDateColumn to a date:

select myDateColumn from myTable 
where to_date(myDateColumn) 
between to_date('13-FEB-11', 'DD-MON-YY') AND TO_DATE('15-FEB-11', 'DD-MON-YY');

which returns the correct results, but it is already a date type! Why do I need to explicitly convert a date column to date before doing the between logical comparison?

The reason why I ask is because this select/ where will be part of a stored procedure selecting data within a specific date range to be run on a big table partitioned by date, with more than ten million rows, and if I can avoid explictly converting each myDateColumn of each row, then I might be able to save some query time, in theory.

Or is there a more correct way to run this comparison to select data within a date range?

Thank you.

Update: Leigh suggested in the answer to diagnose the table for something inconsistent with his query. The result of his query was:

myDateColumn    TO_DATE(myDateColumn)   TO_CHAR(myDateColumn,'DD-MON-YYHH.MI.SSPM') TO_CHAR(myDateColumn,'YYYY')  
14-Feb-11   14-Feb-11   14-FEB-11 12.00.00 AM   0011
14-Feb-11   14-Feb-11   14-FEB-11 12.00.00 AM   0011
14-Feb-11   14-Feb-11   14-FEB-11 12.00.00 AM   0011
14-Feb-11   14-Feb-11   14-FEB-11 12.00.00 AM   0011
14-Feb-11   14-Feb-11   14-FEB-11 12.00.00 AM   0011

Indicating that the reason the between clause was not working, is because none of the data would fall in the query interval, since the year was 0011, during the Roman Empire 🙂

Thanks guys.

Best Answer

Your belief that this should not be necessary is correct based on your assumptions. Normally this means the assumptions should be rechecked (unless there is data corruption or a bug). If you run the following you should get the same results from the first query as the second:

DROP TABLE t1;
CREATE TABLE t1 AS (
   SELECT to_date('01-FEB-2011','DD-MON-YYYY')+level myDateColumn 
   FROM dual CONNECT BY level <=120);

select * from t1 
where myDateColumn 
between to_date('13-FEB-11', 'DD-MON-YY') AND TO_DATE('15-FEB-11', 'DD-MON-YY');

select myDateColumn from t1 
where to_date(myDateColumn) 
between to_date('13-FEB-11', 'DD-MON-YY') AND TO_DATE('15-FEB-11', 'DD-MON-YY');

To check some of the assumptions, can you show the results of the following query?

SELECT myDateColumn, to_date(myDateColumn)
   , to_char(myDateColumn,'DD-MON-YY HH.MI.SS PM'), to_char(myDateColumn,'YYYY') 
FROM myTable
WHERE to_date(myDateColumn)
BETWEEN to_date('13-FEB-11', 'DD-MON-YY') AND TO_DATE('15-FEB-11', 'DD-MON-YY');

The first three columns should all show identical information and the last should verify that the year is correct.

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