“没有先例”常见的英文表达有：
There is no precedent.：这是最直接、常用的表达，简洁明了地传达了“没有先例”这一意思。例如：This situation is completely new; there is no precedent.（这种情况是全新的，没有先例可循。）
There has never been a precedent like this before.：此表达更加强调“以前从未有过这样的先例”，语气稍重一些。例如：The company's decision to merge with its competitor has never been a precedent like this before.（该公司决定与竞争对手合并，这在以前从未有过这样的先例。）