How to create unique index on fields with possible null values (Oracle 11g)?

Question

Here is the sample table with 3 columns (ID, UNIQUE_VALUE, UNIQUE_GROUP_ID)

I want below records can be allowed:

(1, NULL, NULL)
(2, NULL, NULL)
<         


        

Answer 1

You want to only enforce uniqueness on the rows where both UNIQUE_VALUE and UNIQUE_GROUP_ID are not null. To do this, you can use a unique function-based index:

CREATE UNIQUE INDEX func_based_index ON the_table
  (CASE WHEN unique_value IS NOT NULL
         AND unique_group_id IS NOT NULL
        THEN UNIQUE_VALUE || ',' || UNIQUE_GROUP_ID
   END);