Question: Let's look at the following sql query: `SELECT SYSDATE - 0 ParamDateTmp FROM Dual`. I understand that `ParamDateTmp` is just an alias and that `Dual` is a special Oracle table. But I can't understand what result is expected with `SYSDATE - 0`?

Thanks!

Answer: 
SYSDATE - 0 will give you the current date only.

SYSDATE - n will subtract n day's from current date.
As noted by both Jay and Mat, sysdate-0 is simply sysdate.

I have sometimes seen expressions of the form `column-0` as a lazy way of ensuring that 0 is returned in a context where `column` could be null, instead of using COALESCE or its equivalents, such as NVL. However, this shouldn't be a consideration with sysdate, as it should never be null. Possibly just force of habit?