Return value using String result=Command.ExecuteScalar() error occurs when result returns null

There is no need to keep calling .ToString() as getValue is already a string.

Aside that, this line could possibly be your problem:

 string getValue = cmd.ExecuteScalar().ToString();  

If there are no rows .ExecuteScalar will return null so you need to do some checking.

For instance:

var firstColumn = cmd.ExecuteScalar();if (firstColumn != null) {    result = firstColumn.ToString();}

If the first cell returned is a null, the result in .NET will be DBNull.Value

If no cells are returned, the result in .NET will be null; you cannot call ToString() on a null. You can of course capture what ExecuteScalar returns and process the null / DBNull / other cases separately.

Since you are grouping etc, you presumably could potentially have more than one group. Frankly I'm not sure ExecuteScalar is your best option here...

Additional: the sql in the question is bad in many ways:

• sql injection
• internationalization (let's hope the client and server agree on what a date looks like)
• unnecessary concatenation in separate statements

I strongly suggest you parameterize; perhaps with something like "dapper" to make it easy:

int count = conn.Query<int>(  @"select COUNT(idemp_atd) absentDayNo from td_atd    where absentdate_atd between @sdate and @edate    and idemp_atd=@idemp group by idemp_atd",    new {sdate, edate, idemp}).FirstOrDefault();

all problems solved, including the "no rows" scenario. The dates are passed as dates (not strings); the injection hole is closed by use of a parameter. You get query-plan re-use as an added bonus, too. The group by here is redundant, BTW - if there is only one group (via the equality condition) you might as well just select COUNT(1).

Try this one

var getValue = cmd.ExecuteScalar();    conn.Close();return (getValue == null) ? string.Empty : getValue.ToString();