The SQL standard way to implement recursive queries, as implemented e.g. 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.
Edit: apparently the original querant requires a specific example, here's one from the IBM site whose URL I already gave. Given a table:
CREATE TABLE emp(empid INTEGER NOT NULL PRIMARY KEY,
name VARCHAR(10),
salary DECIMAL(9, 2),
mgrid INTEGER);
where mgrid
references an employee's manager's empid
, the task is, get the names of everybody who reports directly or indirectly to Joan
. In Oracle, that's a simple CONNECT
:
SELECT name
FROM emp
START WITH name = 'Joan'
CONNECT BY PRIOR empid = mgrid
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(empid, name) AS
(SELECT empid, name
FROM emp
WHERE name = 'Joan'
UNION ALL
SELECT nplus1.empid, nplus1.name
FROM emp as nplus1, n
WHERE n.empid = nplus1.mgrid)
SELECT name FROM n
Oracle's START WITH
clause becomes the first nested SELECT
, the base case of the recursion, to be UNION
ed 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.