How to correct use the "that"?

His movie won several awards at the film festival, ______ was beyond his wildest dream. (which)

Above is a "non-restrictive attributive clause", and here can't use the "that" other than "which". sometimes I also saw native person write the sentence like this pattern." xxxxxxxx, that xxxxxxxx."" I may go there, that depends"
why there can add the comma symbol before "that". what are the difference for the two sentence? I am confused. how to define this.

I'm going to explain what a restrictive relative and non-restrictive clause are.

A restrictive relative clause (also known as a defining relative clause) gives essential information about a noun that comes before it: without this clause the sentence wouldn’t make much sense. A restrictive relative clause can be introduced by that, which, whose, who, or whom. You should not place a comma in front of a restrictive relative clause:

 She held out the hand which was hurt.

She held out the hand that was hurt.

[main clause] ............>   She held out the hand, She held out the hand         

[restrictive relative clause] ..................> which was hurt, that was hurt.

A non-restrictive relative clause (also called a non-defining relative clause) provides extra information that could be left out without affecting the meaning or structure of the sentence. Non-restrictive relative clauses are normally introduced by which, whose, who, or whom, but never by that. You should place a comma in front of them:

She held out her hand, which Rob shook.

[main clause]..............> She held out her hand

[non-restrictive relative clause]............> which Rob shook

If a non-restrictive relative clause is in the middle of a sentence, you should put commas before and after it:

Bill, who had fallen asleep on the sofa, suddenly roused himself.

[non-restrictive relative clause].............>who had fallen asleep on the sofa

Remember, you CAN’T use ''that'' in non-restrictive relative clause(non-defining relative clause)

Non-defining relative clauses are more often used in written English than in spoken English. You can tell that a clause is non-defining because it is separated by commas at each end of the clause.

Quick Summary:

1. If the clause is restrictive, choose "that" over "which" (about a 99% rule), and don't set the clause off with commas.

2. If the clause is nonrestrictive, choose "which" over "that" and do set the clause off with commas.

A common problem people often have when using relative pronouns is deciding when a relative clause is restrictive or nonrestrictive.

Whether a relative clause is restrictive or nonrestrictive matters for two reasons:

1. Restrictive relative clauses are not set off by commas, while nonrestrictive relative clauses are.

2. As a general rule, the pronoun "that" should be used for restrictive relative clauses, and "which" should be used for nonrestrictive relative clauses.

A nonrestrictive element is set off by commas, as in these examples.

Mr. Smith, who is a well-respected lawyer, has just retired from active practice.

Professor James, who is an expert in Victorian poetry, will be giving a lecture tonight.

MORE EXAMPLES:

Your task, which is to seek out new civilizations and boldly go where no man has gone before, will probably occupy the rest of your adult life.

Kofi Annan, who is the current U.N. Secretary General, has spent much of his tenure working to promote peace in the Third World.

This is Jennifer, who is my college roommate's youngest daughter.

That book, which is the novel I was reading last week, is the one I meant for you to take to the beach with you.

RESTRICTIVE RELATIVE CLAUSES is not set off by commas.

My brother that lives in Arizona is named Pat.

In this sentence the clause "that lives in Arizona" is needed to specify which brother, since the reader has no other way of knowing how many brothers the writer has or which brother is being referred to. (One way to think of the issue of restrictive and non-restrictive elements is that a restrictive element provides information that is necessary to narrow the field of candidates down to one.)

But check out this example:

My other brother, who lives in Texas, is named Sam.

In this sentence the first substantive, the noun phrase "My other brother," conveys the information that the writer has only two brothers, and it also specifies which of those two brothers is being referred to, so the fact that he lives in Texas is extra information--not necessary for specifying which of two brothers is being referred to. In fact, although the brother's name is given in this sentence, the name itself isn't actually needed to narrow the field of candidates to one: the phrase "my other brother" indicates that the writer has only two brothers, and it also specifies which of thoise two brothers he is referring to. (Obviously, the would not say "my other brother" except in a context where he has just referred to the first brother.)

If the relative clause "who lives in Texas" were treated as restrictive, then the sentence would convey the information that the writer has two brothers who live in Texas, and that would only make sense if another brother living in Texas had already been mentioned:

I have two brothers that live in Texas. One is named Eric. My other brother who lives in Texas is named Sam.