thinkphp Forum Post has a new reply after how to be top up?

For example, I have two tables. A T1 table is another T2 that is used to put the theme, and the ID of the T2 that is specifically used to put the reply content to the ID of the T1 to distinguish which subject's reply all the topics are sorted in descending order of time but the posts in the General Forum will be top up if there is a new reply. If I were to design a table like this, how can I get this new post to be topped up? If that's the case, it's $t1->order('time desc')->select() not going to work. So what should I do with a join or something like that, but it's not my design table unreasonable or how? I used the TP

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For example, I have two tables. A T1 table is another T2 that is used to put the theme, and the ID of the T2 that is specifically used to put the reply content to the ID of the T1 to distinguish which subject's reply all the topics are sorted in descending order of time but the posts in the General Forum will be top up if there is a new reply. If I were to design a table like this, how can I get this new post to be topped up? If that's the case, it's $t1->order('time desc')->select() not going to work. So what should I do with a join or something like that, but it's not my design table unreasonable or how? I used the TP

T1 table and add a field last_reply_time represents the last reply time, and then insert T2 and update this field by passing

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