Netezza 中的子查询答案

【问题标题】：Sub-Queries in NetezzaNetezza 中的子查询
【发布时间】：2014-02-21 10:49:21
【问题描述】：

我正在尝试将 SQL 从 Oracle 11 G 移植到 Netezza。

这是我在 Oracle 中的查询：

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')

当我在 Netezza 中运行时出现错误：

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

如何为 Netezza 重写此查询？请帮忙。

【问题讨论】：

您确定您的select 子句(PRIORSCORE) 中的子查询不返回多行吗？
请找到您的答案here。您不能在 SELECT 列表中使用相关子查询。
Maheswaran Ravishankar 是的，我知道我不能使用相关子查询，但是如何为 Netezza 重写？
您的问题在这里得到解答了吗，还是您还有问题？

标签： oracle netezza

【解决方案1】：

我建议将您的代码重写为：

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')

【讨论】：

【解决方案2】：

根据 Netezza Docs

您不能在 SET 操作中使用相关子查询（UNION、INTERSECT、EXCEPT 和 MINUS）。
您不能在具有GROUP BY 和HAVING 子句的聚合中使用相关子查询。
您不能在 ORed 子句或 CASE/WHEN 表达式中使用相关子查询。
您不能在IN 列表中使用相关子查询。
您不能在SELECT 列表中使用相关子查询。

重写查询：(Oracle)（不确定 Netezza 语法）

SELECT
    d1.ID, d1.TEACHERID, d1.CLASS, d1.SECTION, d1.MAJOR, d1.SUPERVISOR, d1.COURSE, d1.SCORE, d1.SCOREDATE, 
    d2.SCORE as PRIORSCORE, 
    (d1.SCOREDATE)-28 as PRIORSCOREDT,
    d1.REMCD
FROM 
    STUDENT_SCORES d1
LEFT JOIN STUDENT_SCORES d2
ON (d2.ID=d1.ID and d2.SCOREDATE = (d1.SCOREDATE)-28 and d1.COURSE=d2.COURSE)
WHERE 
    d1.TEACHERID='T1' AND d1.SCOREDATE=(SELECT MAX(d3.SCOREDATE) FROM STUDENT_SCORES d3 WHERE d3.TEACHERID='T1')

【讨论】：