Question

I have a trigger in Oracle SQL.

CREATE OR REPLACE TRIGGER test
BEFORE INSERT ON SomeTable
FOR EACH ROW
    DECLARE str1 VARCHAR(30);
            str2 VARCHAR(30);
    BEGIN
        -- some code
        IF ( str1 <> str 2 ) THEN
            DBMS_OUTPUT.PUT_LINE( ' if ' );
        ELSE
            DBMS_OUTPUT.PUT_LINE( ' else ' );
        END IF;
    END;

Now, this always goes to the else statement, even when the strings are definitely not equal. I tried to use != instead of <> with the same result. However, it works, in reverse, if I just use

IF ( str1 = str2 ) THEN ... ELSE ... END If;

So what is the right way to test for two strings not being equal to each other (in Oracle)?

Answer 1

Can you show us the actual values being used?
It is possible that the reason for the above behavior is becuase one of the values is null?

If it is possible for str1 and str2 to have null values, your if’s should be like..

IF (str1 is null and str2 is null) then
   <statments depending on whether you want to treat nulls as equal>
else if (
   (str1 is null and str2 is not null) or
   (str2 is null and str1 is not null) or
   (str1 <> str2)) then
  <statements when str1 and str2 are not equal>
else
  <statements when str1 and str2 are equal?
end if;