sqlRouter.GetTableNames will return empty list even if the database does not exist

**Bug Description**

The issue mentions sqlRouter.GetTableNames returning an empty list when a database does not exist. Look for the sqlRouter implementation in the codebase, likely in a router or SQL handling module. Examine the GetTableNames method to understand its error handling and database existence checks. The fix likely involves adding a validation step before returning the table list.

由索引模型根据 Issue 内容生成。