title: rows that violate unique constraints
body: <p>I have a postgres 8.3.4 database. A name table exists with a unique constraint on the triplet UNIQ(name, id, age). Somehow there are several rows that have been added to the database that cause violation of this constraint.</p>
  
  <p>My question is how is this possible ? Shouldn't the database have thrown an error when the first row that would violate the constraint was added ?</p>
  
  <p>name : text<br>
  id : integer not null (fk to a id table)<br>
  age : integer</p>