Question

I need to compare two dates using the Oracle decode function to see if one is less than or equal to the other.

I found this article – http://www.techonthenet.com/oracle/functions/decode.php

Which states (at the bottom) that the below decode function will return date2 if date1 > date2 :

decode((date1 - date2) - abs(date1 - date2), 0, date2, date1)

Would this not return date2 if date1 >= date2 ?

Or is it just if date1 > date2?

Is there an easier solution?

Answer 1

That function will return date2 if date2 <= date1. Plugging in the values and translating to pseudo-code, you get if 0 - 0 = 0 then date2 else date1 where both dates are the same.

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A better solution, if you’re using 8i or later is to use case:

SELECT CASE WHEN date1 >= date2 THEN date2 ELSE date1 END FROM Your_Table;

Since case allows inequality operators, it’s much more readable.

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Or, if you want to be more succinct, you could use the function that’s designed to return the lower of n values:

SELECT LEAST(date1, date2) FROM Your_Table;

(There is also a GREATEST function, which does the opposite.)