firebird的递归查询

with RECURSIVE cte as (  
          select a.* from PM_PROJECT a where a.pm_id='root_id'         
          union all  
          select k.*  from PM_PROJECT k join  cte c on c.pm_id =k.pm_parent
)   
select * from cte 

表结构：

pm_id
pm_parent
pm_name
只可惜，目前只有自上而下的查询。

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SELECT GEN_ID(gen_projectid, 1) FROM RDB$DATABASE;
解决多层自增字段的简单有效办法