Should I check for null or dbnull in the query

Question

I have a query which checks how many records of a certain type are there using count() .

select count(*) from abc where date="some value"

Here, is it possible that my query returns null or DBNull ? Should I check for them?

Answer 1

I don't think so: it can return zero or greater, since you're counting.

NULL would be a wrong result, since no results is there're zero results .

Answer 2

不，它将始终返回一个大于或等于0 。

Answer 3

Just try it:

SELECT COUNT(*) WHERE 1=2
--Returns 0

Per MSDN :

COUNT always returns an int data type value.

Answer 4

If you are using ExecuteScalar, I think the call will retrieve null instead of a DbNull object.

What I use to do in order to always receive a value is encapsulating my request: SELECT ISNULL((SELECT COUNT(date) FROM abc WHERE date = "some value"), 0)

Serge

Answer 5

You should check DbNull as it is database oriented.

See this answer

Answer 6

This is what i do:

if (rdr.HasRows)
        {
          rdr.Read();
          if (rdr["MyField"] != DBNull.Value)
                {
                   bla bla....
                }

So yes check for DBNull.