Question

我有两个问题。

第一个查询如下所示：

SELECT subject_id, period, marks FROM subject_details;

返回以下数据集：

subject_id         period       marks
----------         ------       -----
1                   Jan          50
1                   Feb          40
1                   Mar          30
2                   Jan          60

第二个查询如下：

SELECT subject.subject_id, periods.month, subject.marks  FROM 
(SELECT subject_id, period, marks FROM subject_details) subject,
(WITH PERIOD_COUNTER AS (
SELECT LEVEL-1 AS ID 
FROM DUAL 
CONNECT BY LEVEL <= 6
) 
SELECT TO_CHAR(ADD_MONTHS(TO_DATE('01/01/2011', 'DD/MM/RRRR'), ID),'Mon') 
month FROM PERIOD_COUNTER) periods 
WHERE subject.period (+) = periods.month;


subject_id         period       marks
----------         ------       -----
1                   Jan          50
1                   Feb          40
1                   Mar          30
2                   Jan          60
null                Apr          null
null                May          null
null                Jun          null

如何编写一个可以提供以下结果集的查询（目的是基本上创建一个结果集，填充每个subject_id缺少月份的数据。）：

subject_id         period       marks
----------         ------       -----
1                   Jan          50
1                   Feb          40
1                   Mar          30
1                   Apr          null
1                   May          null
1                   Jun          null
2                   Jan          60
2                   Feb          null
2                   Mar          null
2                   Apr          null
2                   May          null
2                   Jun          null

Answer 1

分区外连接允许您将6个月加入到每个subject_id：

with subject_details as
(
    select 1 subject_id, 'Jan' period, 50 marks from dual union all
    select 1 subject_id, 'Feb' period, 40 marks from dual union all
    select 1 subject_id, 'Mar' period, 30 marks from dual union all
    select 2 subject_id, 'Jan' period, 60 marks from dual
)
select subject_details.subject_id, months.period, subject_details.marks
from
(
    select to_char(add_months(date '2011-01-01', level-1), 'Mon') period
    from dual connect by level <= 6
) months
left outer join subject_details
    partition by (subject_id)
    on months.period = subject_details.period

Answer 2

这是一个UNION电话

SELECT subject_id, period, marks FROM subject_details

UNION

SELECT subject.subject_id, periods.month, subject.marks  FROM 
(SELECT subject_id, period, marks FROM subject_details) subject,
(WITH PERIOD_COUNTER AS (
SELECT LEVEL-1 AS ID 
FROM DUAL 
CONNECT BY LEVEL <= 6
) 
SELECT TO_CHAR(ADD_MONTHS(TO_DATE('01/01/2011', 'DD/MM/RRRR'), ID),'Mon') 
month FROM PERIOD_COUNTER) periods 
WHERE subject.period (+) = periods.month;

Answer 3

你为什么不做笛卡尔式的加入？

我们假设您还有一个表“subjets”和一个表“句点”（有6条记录）


SELECT a.subject_id, b.period
  , (select marks FROM subject_details c 
     where c.subject_id=a.subject_id and c.period = b.period
     ) as marks 
from subjects a, periods b

没试过。

如何编写查询以组合数据？

3 个答案: