title: Select unique rows by max value in column
body: <p>I have a table with timezones which looks like this sample:</p>
  
  <pre><code>CREATE TABLE timezones
  (`CountryCode` varchar(2),
   `ZoneName` varchar(35),
   `Offset` int not null,
   `Dst` char(1),
   `TimeStart` decimal(11,0) not null);
  
  INSERT INTO 
  timezones (`CountryCode`, `ZoneName`, `Offset`, `Dst`, `TimeStart`)
  
  VALUES
  ('VA', 'Europe/Vatican', 7200, '1', 1521939600),
  ('VA', 'Europe/Vatican', 3600, '0', 1540688400),
  ('VA', 'Europe/Vatican', 7200, '1', 1553994000),
  
  ('UA', 'Europe/Zaporozhye', 10800, '1', 1521939600),
  ('UA', 'Europe/Zaporozhye', 7200, '0', 1540688400),
  ('UA', 'Europe/Zaporozhye', 10800, '1', 1553994000),
  
  ('TR', 'Europe/Istanbul', 7200, '0', 1446944400),
  ('TR', 'Europe/Istanbul', 7200, '1', 1459040400),
  ('TR', 'Europe/Istanbul', 10800, '0', 1473195600);
  </code></pre>
  
  <pre>
  +-------------+-------------------+--------+------+------------+
  | CountryCode | ZoneName          | Offset | Dst  | TimeStart  |
  +-------------+-------------------+--------+------+------------+
  | VA          | Europe/Vatican    |   7200 | 1    | 1521939600 |
  | VA          | Europe/Vatican    |   3600 | 0    | 1540688400 |
  | VA          | Europe/Vatican    |   7200 | 1    | 1553994000 |
  | UA          | Europe/Zaporozhye |  10800 | 1    | 1521939600 |
  | UA          | Europe/Zaporozhye |   7200 | 0    | 1540688400 |
  | UA          | Europe/Zaporozhye |  10800 | 1    | 1553994000 |
  | TR          | Europe/Istanbul   |   7200 | 0    | 1446944400 |
  | TR          | Europe/Istanbul   |   7200 | 1    | 1459040400 |
  | TR          | Europe/Istanbul   |  10800 | 0    | 1473195600 |
  +-------------+-------------------+--------+------+------------+
  </pre>
  
  <p>I need to select rows with unique <code>ZoneName</code> field that have the biggest value in <code>TimeStart</code> column.</p>
  
  <p>So for the above table, I expect the following result:</p>
  
  <pre>
  +-------------+-------------------+--------+------+------------+
  | CountryCode | ZoneName          | Offset | Dst  | TimeStart  |
  +-------------+-------------------+--------+------+------------+
  | VA          | Europe/Vatican    |   7200 | 1    | 1553994000 |
  | UA          | Europe/Zaporozhye |  10800 | 1    | 1553994000 |
  | TR          | Europe/Istanbul   |  10800 | 0    | 1473195600 |
  +-------------+-------------------+--------+------+------------+
  </pre>