agg max/min supports char type

// flink
Flink SQL> CREATE TABLE Orders (
>     name char(10),
>     price        DECIMAL(32,2),
>     buyer        ROW<first_name STRING, last_name STRING>,
>     order_time   TIMESTAMP(3)
> ) WITH (
>   'connector' = 'datagen'
> );
[INFO] Execute statement succeed.


Flink SQL> select max(name) from Orders;
[ERROR] Could not execute SQL statement. Reason:
org.apache.flink.table.api.TableException: Max aggregate function does not support type: ''CHAR''.
Please re-check the data type. 

// mysql

CREATE TABLE IF NOT EXISTS `docs` (
  `id` int(6) unsigned NOT NULL,
  `rev` int(3) unsigned NOT NULL,
  `content` char(200) NOT NULL,
  PRIMARY KEY (`id`,`rev`)
) DEFAULT CHARSET=utf8;
INSERT INTO `docs` (`id`, `rev`, `content`) VALUES
  ('1', '1', 'The earth is flat'),
  ('2', '1', 'One hundred angels can dance on the head of a pin'),
  ('1', '2', 'The earth is flat and rests on a bull\'s horn'),
  ('1', '3', 'The earth is like a ball.');

select max(content) from docs;

// result 
|max(content)|
The earth is like a ball.