Question

I have a table in which I need both the values to be primary because I am referencing this combination as foreign key in the other tables. Table definition and the data I need to put are as follows

create table T1
(
  sno number(10),
  desc varchar2(10),
  constraint T1_PK primary key(sno,desc)
)
DATA to put
sno    | desc
---------------------------
100    | "hundred"
000    | null
120    | "one twenty"
123    | ""   <EMPTY STRING>
000    | ""   <EMPTY STRING>

Problem here is desc can be sometimes be null. Primary key can not be null so when I encounter a null value – I’m inserting simply “” in the table. The problem here is some times desc may have empty string.
If I insert the about data 100,Null and 100,”” are two different things but I am not able to put them in the table. I don’t want to put some string like ‘EMPTY’ if null because it may confuse the end user who is looking at the table.

1) How can I handle the null case for desc, while having it as a primary key. I can not use Auto sequence number.
2) How can I distinguish between null string introduced by me and one that is already there?

Answer 1

Why don’t you introduce a real primary key attribute (like id) which is auto incremented and create an index over sno and desc?