在postgresql中，“数据库”和“关系”有什么区别？ （'错误关系x不存在'，'错误数据库x已存在'）

I see the juxtaposition of these two errors and, given the dearth of Google search results, had to ask. What is the difference and what do I need to be doing here?I see the juxtaposition of these two errors and