知っていたら

if I had known

→ 知る
phrase Uncommon #14,286
if I had known The subject is omitted and depends on context; often used for a situation that did not happen.
JA: 知っていたら、教えてあげたのに。
EN: If I had known, I would have told you.

もし彼が彼女の電話番号を知っていたら、電話できるのに。

If he knew her phone number, he could call her.

知っていたら、お話したのですが。

If I’d known, I would have told you.

それを知っていたら、彼女にそんな事を言わなかったのに。

If I'd known that, I wouldn't have said such a thing to her.

もし彼の住所を知っていたら、彼に手紙が書けたのに。

If I had known his address, I could have written him a letter.

あなたがここにいたのを知っていたら、私はすぐきたのに。

If I had known you were here, I would have come right away.

あなたが病気だと知っていたら、病院へ見舞いに行っただろう。

If I had known you were sick, I would have visited you in the hospital.

あのとき彼の名前を知っていたらなあ。

If only I had known his name back then.

もしそれが許されると知っていたら、私は税金など払わなかっただろう。

If I had known I was allowed to do that, I wouldn’t have paid taxes or anything.

これから起きる事をすべて知っていたら-結果は違ってただろう

If I had known everything that was going to happen, the outcome would have been different.

— ピエロがお前を嘲笑う (2014)

もし計画について知っていたら、私は彼の手助けができたのに。

If I had known about the plan, I could have helped him.

彼女の住所を知っていたら、彼女に手紙を書いただろう。

If I had known her address, I would have written her a letter.

知っていたら、彼はもっと早く来たかもしれない。

If he had known, he might have come sooner.

もしそのニュースを知っていたら、君に言っただろうに。

If I had known about that news, I would have told you.

彼は知っていたら来ただろう。

If he had known, he would have come.