Question

Sorry if this is very basic.
Here is what i noticed
Here are the tables:

Table1                         Table2
ID     Value                 ID   Value
1      (null)                 1     0
2      2                      2     2
3      (null)                 3     3

So i used the following statement:

Select T1.ID,T1.Value,T2.value
from
Table1 T1,
Table2 T2
where 
T1.ID=T2.ID
and T1.Value<>T2.Value;

I was expecting the output to show 1,3 ID but it showed nothing not i am confused suppose i want to see all values when one table has null for other table value how can i do that.

Answer 1

Well, the problem is that comparisons to NULL always result in FALSE, except for IS NULL. So the clause should be:

where T1.ID=T2.ID and
      coalesce(T1.Value, t2.value - 1) <> coalesce(T2.Value, t1.value -1);

Or something that matches the NULL values.

By the way, you should also use proper join syntax. So, the query should look more like:

Select T1.ID,T1.Value,T2.value
from Table1 T1 join
     Table2 T2
     on T1.ID=T2.ID and
        ((T1.Value <> T2.Value) or
         (t1.value is not null and t2.value is null) or
         (t1.value is null and t2.value is not null)
        );