Oracle SQL: Comparing Extracted Date in Timestamp

Question

I have the following TABLE.Sample1 :

Col1(varchar) | Col2(timestamp) 
---------------------------------------
A             | 08-NOV-16 09.59.52.000000000 AM
B             | 08-NOV-16 10.05.12.000000000 AM
C             | 09-NOV-16 10.05.12.000000000 AM

Suppose I want to get all rows given a date in the format of DD MON YYYY .

Here's my initial query:

SELECT * 
  FROM Sample1 
 WHERE CAST(Col2 as DATE) = TO_DATE('8 NOV 2016','DD MON YYYY');

I'm curious as to why this query doesn't work on equality( = ) but works fine on inequalities ( > , < , <= , >= , <> ). Am I not comparing the same data types here?

I ended up using TO_CHAR function to make this work but it begs the question, is there a simpler or more direct approach to this?

SELECT * 
  FROM Sample1 
 WHERE TO_CHAR(CAST(Col2 as DATE)) = TO_CHAR(TO_DATE('8 NOV 2016','DD MON YYYY'));

Answer 1

In Oracle a DATE value still has a time. CAST(Col2 as DATE) won't change that.

You can use trunc() to set the time part of a date (or timestamp ) to 00:00:00 and you shouldn't compare strings, but dates:

SELECT * 
FROM Sample1 
WHERE trunc(col2) = TO_DATE('8 NOV 2016','DD MON YYYY');

But I strongly recommend to not use a date format like that. It depends on the NLS settings of the SQL client program and might fail with different language settings.

I prefer using ANSI SQL date literals:

SELECT * 
FROM Sample1 
WHERE trunc(col2) = DATE '2016-11-08';

In both cases, the date will have a time of 00:00:00 because none was given and thus the comparison will work.

Note that trunc(col2) will not be able to use an index on col2 . If performance is important you should either use a range query where col2 >= DATE '2016-11-08' and col2 < DATE '2016-11-09' or create a function based index on trunc(col2) .