时间状语从句前后究竟要不要加逗号?

As I went by,he was .有逗号 When I arrived,they were.有逗号He was singing when I .没有逗号记住：从句部分在前面时,有逗号.从句部分在后面时,没有逗号.She was waiting when I arrived == When I arrived,she w...从句在前面是肯定要用逗号隔开的吗?我也看到过从句在前却没用逗号隔开,所以才感到迷惑放心吧，朋友。你看到的是不规范的英语句子。