This is the first time that anyone has ever 什么从句？
This is the first time in my life that anyone has ever done anything like this for me.
这个是什么从句？是主语从句吗？ that anyone has ever done anything like this for me.是this的内容？

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Rewritten. "No person has ever given me this before. It is the first time in my life."
---“任何人曾经给了我这个之前，这是我有生以来第一次。"

I hope this helps.
It is to say that whatever was done, That individual has never received the item from anyone before. You are the first to give them it, whatever "it" is.

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okay,thank you!

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The clause is used to modify the word "time" (object of the main-sentence "this is X"). And the clause itself is appositive to its onwer, "(the first) time".