如何查询一个项目包含多少个项目？ How to query how many son projects a project contains?

[caibinglin]

我发现projects 表存在一个parent_project_id 字段，但是level存在5级以上，梳理清楚非常困难。
I found a parent_ project_ id field in the projects table , but the level has more than 5 levels, which is very difficult to sort out.