为什么我的 null 检查在 Oracle 的这个 IF 语句中不起作用？

Question

This should be a simple question. I want a particular column claimedby to alternate between a user ID and nothing. So, I'm writing a simple procedure that should look at the column to see if a user ID is in there. If it is, set it to nothing. If it is nothing, then set it to the user ID. That's all I need. But, I'm running into difficulties with determining if the column is nothing. I'm trying various ways, such as 1) case claimedby when null, 2) case claimedby when '', 3) if length(claimedby) < 1. In none of the cases is the column being set to the incoming parameter userID. It's always remaining null. Here's my code:

create or replace PROCEDURE claimprocedure
   ( userID IN varchar2, docketnum IN varchar2 )
IS
   claimed_by varchar2(10);

  cursor c1 is
    SELECT claimedby FROM DR_RULE24.CISR_INTAKE_ERRORS_MASTER 
     WHERE docket_num = docketnum;
     
BEGIN

  open c1;
  fetch c1 into claimed_by;
  close c1;

 DBMS_OUTPUT.PUT_LINE('claimed_by = ' || claimed_by);

CASE claimed_by
    when null then update DR_RULE24.cisr_intake_errors_master set claimedby = userID where docket_num = docketnum;
    when '' then update DR_RULE24.cisr_intake_errors_master set claimedby = userID where docket_num = docketnum;
    ELSE update DR_RULE24.cisr_intake_errors_master set claimedby = '' where docket_num = docketnum;
  END CASE;
  
  if length(claimed_by) < 1 then update DR_RULE24.cisr_intake_errors_master set claimedby = userID where docket_num = docketnum;
    else update DR_RULE24.cisr_intake_errors_master set claimedby = '' where docket_num = docketnum;
   end if;

  if claimed_by = '' then update DR_RULE24.cisr_intake_errors_master set claimedby = userID where docket_num = docketnum;
  else update DR_RULE24.cisr_intake_errors_master set claimedby = '' where docket_num = docketnum;
 end if;

if claimed_by is null then update DR_RULE24.cisr_intake_errors_master set claimedby = userID where docket_num = docketnum;
  else update DR_RULE24.cisr_intake_errors_master set claimedby = '' where docket_num = docketnum;
 end if;
   
END;

I confirm the column is set to null, then I call it with:

SET SERVEROUTPUT ON
call claimprocedure('shone','106712');

The column for docket number 106712 is not being set to 'shone'. I've confirmed that the claimed_by variable in the procedure matches the structure of the claimedby column, which is varchar2(10);

I thought that maybe the IF statements might be canceling each other out. So, I commented out all the ELSE clauses and tried again. It's still null, proving that none of these IF statements are working.

It must be something simple. What am I missing? Thank you.

Answer 1

The case statement (and its cousin the case expression) comes in two forms: the "simple" form and the "searched" form.

The simple form looks like case <expr> when <val1> then... when <val2> then... else... end - this is simple, easy to read, but it only works for direct equality checks. The searched form looks like case when <condition1> then... when <condition2> then... else... end . Here you write a bit more code, but this form is much more general.

Now to your question. You are using the simple form. Its meaning is equivalent to case when claimed_by = null then..... Can you spot the trouble here? If you can't, read again about null , and when something ( anything ) is ever equal to null .

You must use the searched form, and write your condition in the correct, SQL way: case when claimed_by IS null then....