Oracle SQL comparison of DATEs returns wrong result

Question

I have REPORTDATE column in database (DATETIME) type. I want to extract only DATE value from the DATETIME, then to do COUNT

Answer 1

WHERE to_char(REPORTDATE, 'DD.MM.YYYY')>'09.11.2013'

You are comparing two STRINGS. You need to compare the DATEs. As I already said in the other answer here, you need to leave the date as it is for DATE calculations. TO_CHAR is for display, and TO_DATE is to convert a string literal into DATE.

SELECT TO_CHAR(REPORTDATE, 'DD.MM.YYYY'),
  COUNT(*)
FROM TABLE
WHERE REPORTDATE > TO_DATE('09.11.2013', 'DD.MM.YYYY')
GROUP BY TO_CHAR(REPORTDATE, 'DD.MM.YYYY') 

Also, REPORTDATE is a DATE column, hence it will have datetime element. So, if you want to exclude the time element while comparing, you need to use TRUNC

WHERE TRUNC(REPORTDATE) > TO_DATE('09.11.2013', 'DD.MM.YYYY')

However, applying TRUNC on the date column would suppress any regular index on that column. From performance point of view, better use a Date range condition.

For example,

WHERE REPORTDATE
BETWEEN 
        TO_DATE('09.11.2013', 'DD.MM.YYYY')
AND     
        TO_DATE('09.11.2013', 'DD.MM.YYYY') +1

Answer 2

The condition to_char(REPORTDATE, 'DD.MM.YYYY')>'09.11.2013' compare to strings, so 30.10.2013 is after 09.11.2013. You need to compare the dates, not the string values, so you have to change your query to the following.

SELECT to_char(REPORTDATE, 'DD.MM.YYYY') AS MY, COUNT(1) 
from INCIDENT
where trunc(REPORTDATE)> to_date('09.11.2013', 'DD.MM.YYYY')
GROUP BY to_char(REPORTDATE, 'DD.MM.YYYY')

Note: I added a little modification from count(*) to count(1) for optimize the query having the same results.