将条件应用于一个选定的列

Question

我有一个查询，它记录了2018年最后一次记录的事件和记录的事件总数。

在我的查询中，我必须将2018年应用于其中一个列。这是我的代码，让每个人都更容易理解：

select 1 as SortId, 'SouthEast' As "Region", NVL(COUNT(*),0) As "Recordable Events YTD"
from Table_name
WHERE 
IA_TYPE_TEXT IN('con_a','con_b','con_c')
AND
IA_PLANT IN('location_a','location_b','location_c')
AND
to_char(IA_DATE,'YYYY') = '2018' 

这段代码将给我2018年东南部的可记录事件，结果如下：

    SORTID Region    Recordable Events YTD
---------- --------- ---------------------
         1 SouthEast                     0

这是我的第二个查询，显示东南地区的最后一个事件

Select To_CHAR(TRUNC(max(IA_Date)),'MM/DD/YYYY') As "Incident Date"
from DOT.IA_LOG where IA_TYPE_TEXT IN('con_a','con_b','con_c')
AND
IA_PLANT IN('location_a','location_b','location_c')

结果是：

Incident Date
-------------
12/18/2017

我试图在一个结果中显示所有数据，但是当我尝试将第二个select语句添加到第一个时，它给出了我最后一个事件日期的空结果，因为2018条件适用于它这里是我的组合查询和结果。

select 1 as SortId, 'SouthEast' As "Region", NVL(COUNT(*),0) As "Recordable Events YTD",
  To_CHAR(TRUNC(max(IA_Date)),'MM/DD/YYYY') As "Last Recordable Event" 
from Table_name
WHERE 
IA_TYPE_TEXT IN('con_a','con_b','con_c')
AND
IA_PLANT IN('location_a','location_b','location_c')
AND
to_char(IA_DATE,'YYYY') = '2018' 

    SORTID Region    Recordable Events YTD Last Recordable Event
---------- --------- --------------------- ---------------------
         1 SouthEast                     0

如何将条件应用于其中一列？最简单的方法是什么？

Answer 1

请改用cte（common table expression）。希望这可以帮助。谢谢。

 with tmp as (select 1 as SortId, 
'SouthEast' As  rgn,
NVL(COUNT(*),0) As YTD
from Table_name
WHERE IA_TYPE_TEXT IN('con_a','con_b','con_c')
AND IA_PLANT IN('location_a','location_b','location_c')
AND to_char(IA_DATE,'YYYY') = '2018')
select tmp.SortId, 
rgn as "Region",
YTD as "Recordable Events YTD",
To_CHAR(TRUNC(max(IA_Date)),'MM/DD/YYYY') As "Incident Date" 
from DOT.IA_LOG, tmp
where IA_TYPE_TEXT IN('con_a','con_b','con_c')
AND IA_PLANT IN('location_a','location_b','location_c')
group by sortid,rgn,ytd

Result:
SortId  Region      Recordable Events YTD   Incident Date
1       SouthEast   0                       12/18/2017

Answer 2

您可以使用条件计数，在count函数调用中使用case表达式，即：

COUNT(CASE WHEN to_char(IA_DATE,'YYYY') = '2018' then IA_DATE END)

而且没有全年的整体过滤器;原位：

select 1 as SortId,
  'SouthEast' As "Region",
  NVL(COUNT(CASE WHEN to_char(IA_DATE,'YYYY') = '2018' then IA_DATE END),0)
    As "Recordable Events YTD",
  To_CHAR(TRUNC(max(IA_Date)),'MM/DD/YYYY') As "Last Recordable Event" from IA_LOG
WHERE 
IA_TYPE_TEXT IN('con_a','con_b','con_c')
AND
IA_PLANT IN('location_a','location_b','location_c')
/

count函数只计算非空值;如果不满足条件，则case表达式的结果为null，因此不计算这些行。

使用虚拟数据可以得到您在问题中显示的相同结果，这会得到：

    SORTID Region    Recordable Events YTD Last Recordable Event
---------- --------- --------------------- ---------------------
         1 SouthEast                     0 12/18/2017

不直接相关，但我个人更喜欢使用extract()来比较部分日期; count()不能返回null因此不需要nvl();因为你的格式模型不包括时间，所以也不需要trunc()。所以你可以略微简化为：

select 1 as sortid,
  'SouthEast' as "Region",
  count(case when extract(year from ia_date) = 2018 then ia_date end)
    as "Recordable Events YTD",
  to_char(max(ia_date), 'MM/DD/YYYY') as "Last Recordable Event"
from ia_log
where ia_type_text in('con_a', 'con_b', 'con_c')
and ia_plant in('location_a', 'location_b', 'location_c')

得到相同的结果。我也避免引用标识符，但可能会直接用于显示。