title: How can a primary key column have duplicated values in Oracle?
body: <p>I have just tried to import an Oracle DB to another and it gave an error tells that duplicated values found in a primary key column. Then I checked the source table, and yes really there are duplicate values in PK, and checked PK is enabled and normal. Now I wonder how can this happen.</p>
  
  <p>Edit: I found that index is in unusable state. I don't know how did it happen, just found this:
  <a href="http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:1859798300346695894" rel="noreferrer">http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:1859798300346695894</a></p>