要是【yàoshi】

要是 means "if" and works like 如果: the condition comes first, and 就 goes before the verb of the result. 要是 belongs to conversation; 如果 is the neutral word that also suits writing.

When both clauses have the same subject, it often goes before 要是.

的话 can close the condition, as it does after 如果.

就 after the subject

就 is an adverb and goes after the subject of the result clause, not before it.

• × 要是你去，就我去 → 要是你去，我就去

要是…就好了

要是 + something that isn't true + 就好了 is a wish: "if only".

The same frame without 就好了 talks about what would have happened, with 了 at the end.