How to check DB table values in SQL stored procedure with C#

Question

May I know how to check the values in a database table when there is no exist data?

I wrote this SQL script and C# code to test the condition statement. But it doesn't work.

In SQL stored procedures I have tried Select * from Table and check if the condition is 0

DECLARE @CheckFindQTY FLOAT 

SET @CheckFindQTY = (SELECT INV_QTY FROM OTH_INV_QTY_LOC 
                     WHERE INV_ID = @INV_ID 
                       AND INV_LOCATION = @INV_LOCATION  
                       AND INV_QTY = @INV_QTY)

IF @CheckFindQTY = 0
BEGIN
    SELECT @RecordFound = 3
END

And also I tried checking if the condition is NULL

DECLARE @CheckFindQTY FLOAT 

SET @CheckFindQTY = (SELECT INV_QTY 
                     FROM OTH_INV_QTY_LOC 
                     WHERE INV_ID = @INV_ID 
                       AND INV_LOCATION = @INV_LOCATION  
                       AND INV_QTY = @INV_QTY)

IF @CheckFindQTY = NULL
BEGIN
     SELECT @RecordFound = 3
END

Then I query the condition in C# if the condition is == 3 then show alert message

int recordFound = Convert.ToInt32(_cmd.Parameters["@RecordFound"].Value);

if (recordFound == 3)
{
   ScriptManager.RegisterStartupScript(this, this.GetType(), "Message", "alert('There is not QTY in Location, please check again!!')", true);
}

Answer 1

DECLARE @CheckFindQTY as FLOAT = NULL;
SELECT @CheckFindQTY = INV_QTY FROM OTH_INV_QTY_LOC WHERE INV_ID=@INV_ID AND INV_LOCATION = @INV_LOCATION AND INV_QTY=@INV_QTY;

IF @CheckFindQTY is NULL
  SELECT @RecordFound = 3

Note that the test for a NULL value is IS NULL, not = NULL.