从Oracle迁移到SQL Server

Question

I have the following query written with Oracle

delete from EQUI_HIERARCHY; 

select max(level) into v_max_depth 
from EQUIP_D

connect by prior EQUIP_NO=PARENT_EQUIP_NO 
start with PARENT_EQUIP_NO is null; 

How to transform it into SQL Server ?

Answer 1

The SQL standard way to implement recursive queries, as implemented eg by IBM DB2 and SQL Server , is the WITH clause. See this article for one example of translating a CONNECT BY into a WITH (technically a recursive CTE) -- the example is for DB2 but I believe it will work on SQL Server as well.

In SQL Server , IBM DB2, or PostgreSQL 8.4 (as well as in the SQL standard, for what that's worth;-), the perfectly equivalent solution is instead a recursive query (more complex syntax, but, actually, even more power and flexibility):

    WITH n(v_max_depth ) AS 
         (SELECT max(level)
          FROM EQUIP_D
          WHERE PARENT_EQUIP_NO IS NULL
               UNION ALL
          SELECT max(level)
          FROM EQUIP_D as nplus1, n
          WHERE n.EQUIP_NO= nplus1.PARENT_EQUIP_NO)

   SELECT max(v_max_depth) FROM n

Oracle's START WITH clause becomes the first nested SELECT , the base case of the recursion, to be UNIONed with the recursive part which is just another SELECT .

SQL Server's specific flavor of WITH is of course documented on MSDN , which also gives guidelines and limitations for using this keyword, as well as several examples.