这句话有没有错误？帮我改正

He had always been engaged in doing database development in those companies, for which he had worked since he graduated.

He always had been engaged in database development in those companies he had worked since he graduated.

逗号和for都去掉

1. He always had been engaged ... 改为：He had always been engaged ...

2. for which he worked since ... 改为：for which he have worked since ...

逗号去掉,直接改成since his graduation
这样更简洁点.

只是建议~ 原句也没错