Obvious inefficiencies in this Netezza query?
I have noticed that the optimizer doesn't enforce the constraints on left joins efficiently.  I have success in this situation by forcing the constraints in sub queries.  Consider revising your query like below:

CREATE TABLE T3 AS
SELECT 
        A.*, 
        COALESCE(C.FIELD1,0) AS FIELD1A,
        COALESCE(B.FIELD2,0) AS FIELD2A,
        COALESCE(B.FIELD3,0) AS FIELD3A,
        COALESCE(C.FIELD4,0) AS FIELD4A,
        COALESCE(C.FIELD5,0) AS FIELD5A,
        B.KEY1,
        COALESCE(C.FIELD6,0) AS FIELD6A
FROM T1 A
LEFT JOIN 
(select * from T2 where TIMEFIELD1 &lt;= DATE '28FEB2013'
AND  TIMEFIELD2 &gt; DATE '28FEB2013'
AND  FIELD7= 'X' ) B
ON   A.KEY2 = B.KEY1 
LEFT JOIN 
(select * from T2  where AND  TIMEFIELD1  &lt;= DATE '28FEB2013'
AND  TIMEFIELD2 &gt; DATE '28FEB2013'
AND  FIELD7= 'X') C
ON   A.KEY3 = C.KEY1 


DISTRIBUTE ON RANDOM