comment (chain operation 16)

For example

Db::table('think_score')->comment('查询考试前十名分数')
    ->field('username,score')
    ->limit(10)
    ->order('score desc')
    ->select();

The final generated SQL statement is:

SELECT username,score FROM think_score ORDER BY score desc LIMIT 10 /* 查询考试前十名分数 */