在 case when 语句中使用计算列结果

Question

我正在使用 Oracle SQL Developer，我有一个声明

select 
c.name as "Customer Name"
cy.country as "Country",
c.startdateutc as "UTC Start Date"
case when c.startdateutc >= To_date('2023-03-12 08:00', 'YYYY-MM-DD hh24:mi') and c.startdateutc <= To_date('2023-11-05 07:00', 'YYYY-MM-DD hh24:mi') then c.startdateutc  - 5/24
else c.startdateutc - 6/24 END AS "New Start Date"
from
customer c
left join country cy
on cy.id = c.countryid
where c.startdateutc >= date '2020-07-01'

我想根据类似于此的 Case When Column 创建另一个列

case when New Start Date >= To_date('2023-03-12 08:00', 'YYYY-MM-DD hh24:mi') and New Start Date <= To_date('2023-11-05 07:00', 'YYYY-MM-DD hh24:mi') then New Start Date  - 5/24
else New Start Date - 6/24 END AS "New Calc Start Date"

提前致谢

Answer 1

一个选项是嵌套 CASEs:

select 
  case when 
            case when     c.startdateutc >= To_date('2023-03-12 08:00', 'YYYY-MM-DD hh24:mi') 
                      and c.startdateutc <= To_date('2023-11-05 07:00', 'YYYY-MM-DD hh24:mi') 
                 then c.startdateutc  - 5/24
                 else c.startdateutc - 6/24 
            END 
       then something
  else something_else
end new_case_column
from ...

另一种是将当前查询用作子查询（或 CTE），例如

with current_query as
  (select 
   c.name as "Customer Name"
   cy.country as "Country",
   c.startdateutc as "UTC Start Date"
   case when c.startdateutc >= To_date('2023-03-12 08:00', 'YYYY-MM-DD hh24:mi') and    
             c.startdateutc <= To_date('2023-11-05 07:00', 'YYYY-MM-DD hh24:mi') then 
             c.startdateutc  - 5/24
        else c.startdateutc - 6/24 
   END AS new_start_date
   from
   customer c
   left join country cy
   on cy.id = c.countryid
   where c.startdateutc >= date '2020-07-01' 
)
select case when new_start_date = something then something
            else something else
       end
from current_query join ...

Answer 2

考虑像这样使用子查询：

SELECT COLUMNNAMES
FROM (
    SELECT COLUMNNAMES
    FROM TABLEname2
    WHERE condition
    ) t

在这种情况下：

SELECT 
    t.*
    ,CASE 
        WHEN New_Start_Date >= To_date('2023-03-12 08:00', 'YYYY-MM-DD hh24:mi')
            AND New_Start_Date <= To_date('2023-11-05 07:00', 'YYYY-MM-DD hh24:mi')
            THEN New_Start_Date - 5 / 24
        ELSE New_Start_Date - 6 / 24
        END AS "New Calc Start Date"
FROM (
    SELECT c.name AS "Customer Name"
        ,cy.country AS "Country"
        ,c.startdateutc AS "UTC Start Date" 
        ,CASE 
            WHEN c.startdateutc >= To_date('2023-03-12 08:00', 'YYYY-MM-DD hh24:mi')
                AND c.startdateutc <= To_date('2023-11-05 07:00', 'YYYY-MM-DD hh24:mi')
                THEN c.startdateutc - 5 / 24
            ELSE c.startdateutc - 6 / 24
            END AS "New_Start_Date"
    FROM customer c
    LEFT JOIN country cy ON cy.id = c.countryid
    WHERE c.startdateutc >= DATE '2020-07-01'
    ) t

在 case when 语句中使用计算列结果

Use calculated column result in case when statement

sql

oracle

conditional-statements

oracle-sqldeveloper