6  

This should work but is probably slow:

这应该工作，但可能很慢：

CREATE temporary table seq ( id int, seq int);
INSERT INTO seq ( id, seq )
    SELECT id, 
      (SELECT count(*) + 1 FROM test c 
      WHERE c.id < test.id AND c.account = test.account) as seq 
    FROM test;

UPDATE test INNER join seq ON test.id = seq.id SET test.seq = seq.seq;

I have called the table 'test'; obviously that needs to be set correctly. You have to use a temporary table because MySQL will not let you use a subselect from the same table you are updating.

我把表称为“测试”;显然需要正确设置。您必须使用临时表，因为MySQL不允许您使用您正在更新的同一个表中的子选择。

5  

Create a trigger:

创建一个触发器：

CREATE TRIGGER trg_mytable_bi
BEFORE INSERT ON mytable
FOR EACH ROW
BEGIN
      DECLARE nseq INT;
      SELECT  COALESCE(MAX(seq), 0) + 1
      INTO    nseq
      FROM    mytable
      WHERE   account = NEW.account;
      SET NEW.seq = nseq;
END;

5  

The question is tagged as "mysql", so yes, MySQL's auto_increment can create groupwise sequential ids.
see http://dev.mysql.com/doc/refman/5.0/en/example-auto-increment.html:

这个问题被标记为“mysql”，所以是的，MySQL的auto_increment可以创建groupwise顺序id。请参阅http://dev.mysql.com/doc/refman/5.0/en/example-auto-increment.html：

For MyISAM and BDB tables you can specify AUTO_INCREMENT on a secondary column in a multiple-column index. In this case, the generated value for the AUTO_INCREMENT column is calculated as MAX(auto_increment_column) + 1 WHERE prefix=given-prefix. This is useful when you want to put data into ordered groups.

edit: example php script (using PDO, but it's the same game with the php-mysql module)

编辑：示例php脚本（使用PDO，但它与php-mysql模块的游戏相同）

$pdo = new PDO('mysql:host=...;dbname=...', '...', '...'); 
$pdo->setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION );

// example table
$pdo->exec(
  'CREATE TEMPORARY TABLE Foo (
    id int auto_increment,
    account int,
    someotherstuff varchar(32),
    primary key(account,id)
  ) engine=MyIsam'
);
// insert example data
$stmt = $pdo->prepare('INSERT INTO Foo (account,someotherstuff) VALUES (?,?)');
$stmt->execute(array(1, '1a'));
$stmt->execute(array(1, '1b'));
$stmt->execute(array(1, '1c'));
$stmt->execute(array(2, '2a'));
$stmt->execute(array(2, '2b'));
$stmt->execute(array(1, '1d'));
unset($stmt);

// query data
foreach( $pdo->query('SELECT account,id,someotherstuff FROM Foo') as $row ) {
  echo $row['account'], ' ', $row['id'], ' ', $row['someotherstuff'], "\n";
}

prints

版画

1 1 1a
1 2 1b
1 3 1c
2 1 2a
2 2 2b
1 4 1d