title: Liquibase: deleting duplicate row
body: <p>I'm writing a new changeset to define a unique key on my table, but it appears a previous changeset inserts duplicated rows in my table (by duplicated, I mean two entries with the same value on the target column of my new unique constraint).</p>
  
  <p>Because of production constraints, I cannot modify previous changesets.</p>
  
  <p>So, before adding my constraint, I want to delete the duplicated row.</p>
  
  <p>Here is my changeset:</p>
  
  <pre><code>{
      "changeSet": {
          "id": "123",
          "author": "me",
          "changes": [
              {
                  "delete": {
                      "tableName": "foo",
                      "where": "name = 'myname'"
                  }
              },
              {
                  "insert": {
                      "tableName": "foo",
                      "columns": [
                          {
                              "column": {
                                  "name": "id",
                                  "valueSequenceNext" : "foo_seq"
                              }
                          },
                          {
                              "column": {
                                  "name": "name",
                                  "valueComputed": "myname"
                              }
                          }
                      ]
                  }
              },
              {
                  "addUniqueConstraint": {
                      "columnNames": "name",
                      "constraintName": "uk_fooname",
                      "tableName": "foo"
                  }
              }
          ]
      }
  </code></pre>
  
  <p>Let's say my duplicated entries hold the name 'myname'. As you see, I'm deleting all duplicated entries then I have to reinsert my unique entry.</p>
  
  <p>I would have to delete only one of the duplicated row in my delete statement, rather than deleting both then inserting again. But I cannot find any solution to put a where condition on the row_number.</p>
  
  <p><strong>Anyone knows how to add to the where clause the row number?</strong></p>
  
  <p>Thanks for your help.</p>