How to get row count when a particular field is empty

RowID       TimeReceived    TimeRead    tbl_user_UserID     tbl_message_MsgID

  5     2011-09-06 11:16:20   NULL               2                1
  6     2011-09-06 11:17:04   NULL               3                1
  7    开发者_如何学Go 2011-09-06 11:17:19   NULL               100              1

This is my table

 command = new MySqlCommand("SELECT COUNT(Distinct RowID) FROM tbl_usermessage WHERE TimeRead= NULL AND tbl_message_MsgID=@Value1", connectionString);
         command.Parameters.Add("@value1", MySqlDbType.Int32, 25);
         command.Parameters["@value1"].Value = MessageID;
         int nnnID = Convert.ToInt32(command.ExecuteScalar());

I want to count the row where time read is null, it gives me 0 as output where it should be 3. Where am I going wrong. i have set the default value for time read as null.

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Query for getting count

select count(Distinct RowID) from table where TimeRead is null

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Use "is NULL" instead of "= NULL"

SELECT COUNT(Distinct RowID) FROM tbl_usermessage WHERE TimeRead is NULL ...

Also check if your parameter @value1 is correct!

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Your SQL is incorrect. You can check for NULL by using IS NULL:

 command = new MySqlCommand("SELECT COUNT(Distinct RowID) FROM tbl_usermessage WHERE TimeRead IS NULL AND tbl_message_MsgID=@Value1", connectionString);
         command.Parameters.Add("@value1", MySqlDbType.Int32, 25);
         command.Parameters["@value1"].Value = MessageID;
         int nnnID = Convert.ToInt32(command.ExecuteScalar());