OK, found an old mailing thread i posted, here's a working setting to quarantine clean message into SQL database. Steps:

1: Add below settings in /etc/amavisd/amavisd.conf:

$clean_quarantine_method = 'sql:';
$clean_quarantine_to = 'clean-quarantine';

2: Find policy bank 'MYUSERS', append two lines in this policy bank:

$policy_bank{'MYUSERS'} = {
    ...
    clean_quarantine_method => 'sql:',
    final_destiny_by_ccat => {CC_CLEAN, D_DISCARD},
}

3: Make sure you have '@storage_sql_dsn' enabled. For example:

@storage_sql_dsn = (
    ['DBI:mysql:database=amavisd;host=127.0.0.1;port=3306', 'amavisd', 'qAv9CYva0vHA1GCX0J9f23WJvqRzt7'],
);

4: Restart Amavisd service.

That's all. Now all clean emails sent by your mail users will be quarantined into SQL database. if you have iRedAdmin-Pro, you can manage (release or delete) quarantined emails with it. Screenshot of iRedAdmin-Pro for your reference: