title: Oracle update: ORA-01427: single-row subquery returns more than one row
body: <pre><code>UPDATE TMP_COLUMNS 
      SET COLUMNNAME = (SELECT COLUMN_NAME FROM 
                        user_tab_columns usertable
                        WHERE
                        table_name = table_Name
                        AND usertable.column_id = TMP_COLUMNS.idcolumn)
      WHERE EXISTS (SELECT COLUMN_NAME 
                    FROM 
                    user_tab_columns usertable
                    WHERE
                    table_name = table_Name
                    AND usertable.column_id = TMP_COLUMNS.idcolumn);
  
      COMMIT;
  </code></pre>
  
  <p>I am getting the error <code>ORA-01427: single-row subquery returns more than one row</code></p>