Supplying row value as column name

Question

Hi all,
I have two tables in which row value in one table is column name of other. How do i relate it to retreive the data...
Table 1: control (contains 3 columns in it)
table_name - parametername - parametervalue
MI     - UNPROCESSED_FLAG -     N
MI     - PROCESSED_FLAG - Y
MI     - FROM_DATE     - 01-JAN-2008
MI     - TO_DATE     - 31-DEC-2010
EMP     - DEPTNO     - 30
EMP     - JOB     - SALESMAN
EMP     - FROM_DATE     - 01-JAN-1982
EMP     - TO_DATE     - 31-DEC-1995
Table 2: emp (contains the columns: empno,ename,deptno,job,hiredate)
I want to display all details from emp table according to the parameter given in control table. I have already written a query using subquery
select *
from emp
where
deptno = (select parameter_value from job_control where parameter_name = 'DEPTNO')
and
job = (select parameter_value from job_control where parameter_name = 'JOB')
and
hiredate between (select parameter_value from job_control where parameter_name = 'FROM_DATE' and table_name = 'EMP') and (select parameter_value from job_control where parameter_name = 'TO_DATE' and table_name = 'EMP');
But i want to write ot using joins. Plz help me out.....
Thanks

Answer 1

Hi,
Welcome to the forum!
Whenever you have a question, please post CREATE TABLE and INSERT statements for your sample data, so that the people who want to help you can re-create the problem and test their ideas. (There's no need to post commonly available tables. like those in the scott schema, but make it clear which such tables you're using.) Since this is your first post, I'll do it for you:
CREATE TABLE     control_table
     table_name     VARCHAR2 (20)
,     parametername     VARCHAR2 (20)
,     parametervalue     VARCHAR2 (20)
INSERT INTO control_table (table_name, parametername, parametervalue) VALUES ('EMP', 'DEPTNO',       '30');
INSERT INTO control_table (table_name, parametername, parametervalue) VALUES ('EMP', 'JOB',       'SALESMAN');
INSERT INTO control_table (table_name, parametername, parametervalue) VALUES ('EMP', 'FROM_DATE', '01-SEP-1981');
INSERT INTO control_table (table_name, parametername, parametervalue) VALUES ('EMP', 'TO_DATE',       '31-DEC-1995');
INSERT INTO control_table (table_name, parametername, parametervalue) VALUES ('MI',  'FROM_DATE', '01-JAN-2008');
;Also post the exact results you want from that sample data. The query below produces these results from the control_table above and the standard scott.emp table:
EMPNO ENAME      JOB         MGR HIREDATE    SAL  COMM DEPTNO
7654 MARTIN     SALESMAN   7698 28-SEP-81  1250  1400     30
7844 TURNER     SALESMAN   7698 08-SEP-81  1500     0     30Always say which version of Oracle you're using. The query below works in Oracle 9.1 and up.
One thing you can do is pivot the appropriate parameters into a one-row result set, and treat it as a table, like this:
WITH     got_params     AS
     SELECT  TO_NUMBER (MIN (CASE WHEN parametername = 'DEPTNO'    THEN parametervalue END))               AS deptno
     ,             MIN (CASE WHEN parametername = 'JOB'       THEN parametervalue END)               AS job
     ,     TO_DATE   (MIN (CASE WHEN parametername = 'FROM_DATE' THEN parametervalue END), 'DD-MON-YYYY')     AS fromdate
     ,     TO_DATE   (MIN (CASE WHEN parametername = 'TO_DATE'   THEN parametervalue END), 'DD-MON-YYYY')     AS todate
     FROM     control_table
     WHERE     table_name     = 'EMP'
SELECT  e.*
FROM     emp         e
JOIN     got_params  p  ON   e.deptno     = p.deptno
                 AND  e.job     = p.job
                 AND  e.hiredate     BETWEEN  p.fromdate
                                    AND      p.todate
;This assumes that the combination (table_name, parametername) is unique in the control_table.