title: Adding existing column as primary key in DB2 with existing primary keys
body: <p>I have a table MY_TABLE in DB2 containing several columns:</p>
  
  <pre><code>PRODUCT_ID
  ADDED_DT
  PRODUCT_NAME
  PRODUCT_COLOR
  PRODUCT_PRICE
  EXPIRY_DT
  </code></pre>
  
  <p>Out of these columns, below columns form the primary key:</p>
  
  <pre><code>PRODUCT_ID
  ADDED_DT
  </code></pre>
  
  <p>I want to add EXPIRY_DT as primary key such that the table will now have three primary keys viz. PRODUCT_ID, ADDED_DT and EXPIRY_DT</p>
  
  <p>I tried below set of commands:</p>
  
  <pre><code>ALTER TABLE MY_TABLE ADD PRIMARY KEY (EXPIRY_DT);
  REORG TABLE MY_TABLE;
  </code></pre>
  
  <p>However, the query failed with error:</p>
  
  <pre><code>Table "MY_TABLE" already has a "PRIMARY" key.
  </code></pre>
  
  <p>How to acheive this ?</p>