title: How to give a unique constraint to a combination of columns in Oracle?
body: <p>I have a Table with 4 Columns</p>
  
  <p>Each Column will be A,B,C,D</p>
  
  <p>Column A is the Primary key.
  Column B has unique name constraint.</p>
  
  <p>Now I want to remove the unique constraint for column B and give a unique constraint by combining the columns B, C and D. So the table will allow only one row with a particular value in columns B,C and D.</p>
  
  <p>How can I give this type of a constraint?</p>
  
  <p>I tried giving the composite unique key like : </p>
  
  <pre><code>ALTER TABLE TABLENAME ADD CONSTRAINT CONSTRAINT_NAME UNIQUE (COLUMN_B, COLUMN_C, COLUMN_D)
  </code></pre>
  
  <p>But it is checking whether any one of the constraint is present rather than checking for the combination of unique key constraint.</p>