Question

I tried @somevalue = null and it worked that time. But now its not working. How to check if the value is null?
In brief what I need to do is if @existPerson is equal to null then INSERT the values into the database. But if it exists then return -2. I have checked in the database made sure that there are no same value as @nic = 100. Even so its returning me -2. What could be the possible reason ? Thanks a lot!

CREATE PROCEDURE [dbo].[addStudent] 
    @stuName varchar(50), 
    @address varchar(100),
    @tel varchar(15),
    @etel varchar(15),
    @nic varchar (10),
    @dob date


AS 
BEGIN   
    SET NOCOUNT ON;

    DECLARE @currentID INT
    DECLARE @existPerson INT
    SET @existPerson = (SELECT p_ID FROM Student WHERE s_NIC = @nic);
    IF @existPerson = null
        BEGIN
            INSERT INTO Person (p_Name, p_RegDate, p_Address, p_Tel, p_EmergeNo, p_Valid, p_Userlevel)
            VALUES (@stuName,  GETDATE(), @address, @tel, @etel, 0, 'Student' );
            SET @currentID = (SELECT MAX( p_ID) FROM Person); 
            INSERT INTO Student (p_ID, s_Barcode, s_DOB, s_NIC) VALUES (@currentID , NULL, @dob, @nic);
            return 0;
        END
    ELSE
        return -2;
END 

Answer 1

this should be

  IF @existPerson is null

in sql if you want to check value is null or not than you need use is null or is not null instead of = null or <> null