Oracle Unique Constraint based on column value

Question

I have the following unique constraint

dup_Checklist_QNum UNIQUE (QUESTION_NO, IS_ACTIVE)

I am trying to prevent two questions having the s

Answer 1

You can create a unique function-based index

CREATE UNIQUE INDEX idx_dup_active
    ON <<table name>>( CASE WHEN is_active = 1
                            THEN question_no
                            ELSE NULL
                        END );

This takes advantage of the fact that Oracle b-tree indexes do not store data where the leaf block data would be entirely NULL.