关系型数据库 presql 不支持执行DDL sql，如何解决

关系型数据库 前置sql可能有几种应用场景，如：写入表还未创建，或写入表需补充字段。 此时，可以在前置sql编写DDL sql。 但目前会先检查写入表，然后才执行 presql，所以不能支持。

Start by tracing how relational database writers handle presql and when they validate the destination table. Confirm whether DDL presql must run before that validation, then define completion as allowing a missing table or required-column change to be handled by presql before the write proceeds. No source files or tests are named in the issue.

Written by the indexing model from the issue text.