Sub-Queries in Netezza

Question

I am trying to port a SQL from Oracle 11 G to Netezza.

Here is my query in Oracle:

SELECT
    ID, TEACHERID, CLASS, SECTION, MAJOR, SUPERVISOR, COURSE, SCORE, SCOREDATE, 
    (select SCORE from STUDENT_SCORES d2 where d2.ID=d1.ID and d2.SCOREDATE (d1.SCOREDATE)-28 and d1.COURSE=d2.COURSE)  as PRIORSCORE, 
    (d1.SCOREDATE)-28 as PRIORSCOREDT,
    REMCD
FROM 
    STUDENT_SCORES d1
WHERE 
    TEACHERID='T1' AND SCOREDATE=(SELECT MAX(SCOREDATE) FROM STUDENT_SCORES WHERE TEACHERID='T1')

When I run this in Netezza I get an error:

ERROR:  (2) This form of correlated query is not supported - consider rewriting

How do I rewrite this query for Netezza? Please help.

Answer 1

I would suggest rewriting your code to this:

select d1.ID, d1.TEACHERID, d1.CLASS, d1.SECTION, d1.MAJOR, d1.SUPERVISOR, d1.COURSE, d1.SCORE, d1.SCOREDATE
,d2.SCORE as PRIORSCORE
,d2.SCOREDATE as PRIORSCOREDT
,d1.REMCD
from STUDENT_SCORES d1 left outer join
(select * from STUDENT_SCORES ss where ss.SCOREDATE = (SELECT MAX(SCOREDATE)-28 FROM STUDENT_SCORES WHERE TEACHERID='T1') d2
on  d1.ID=d2.ID
and d1.COURSE=d2.COURSE
where d1.TEACHERID='T1'
and d1.SCOREDATE = (SELECT MAX(SCOREDATE) FROM STUDENT_SCORES WHERE TEACHERID='T1')