问题
I have a table which contains the following fields
- Supervisorid
- Empid
This is just like a referral program. A guy can refer 3 guys under him i.e, 3 is referring three guys namely 4 5 8 similarly 4 is referring 9 10 and 11 likewise 8 is referring 12, 13 it goes like this..
I want a query to get all EmpId under Supervisor 3
回答1:
Do you want us to write the solution for you, or explain a bit how recursive queries can be built up ?
An example of how they are built up is on http://publib.boulder.ibm.com/infocenter/db2luw/v8//topic/com.ibm.db2.udb.doc/ad/samples/clp/s-flt-db2.htm.
The IBM DB2 redbook has an entire chapter on SQL recursion.
The gist is that the following steps are generally involved:
you define a "seed". SELECT SUPID, EMPID, 1 AS LVL FROM EMP WHERE SUPID = 3;
you assign to this a name. WITH SRC AS <your seed here>
you define the way to go to the 'next level', starting from the seed, using the assigned name. SELECT SRC.SUPID, F.EMPID, SRC.LVL+1 FROM SRC, EMP WHERE SRC.EMPID=EMP.SUPID
you combine the two together (inside the WITH clause) WITH SRC AS <your seed here> UNION ALL <the other SELECT here>
(optionally) you define which columns to select. SELECT EMPID, LVL FROM SRC.
来源：https://stackoverflow.com/questions/3995393/recursive-query