Clarion 中的 PostgreSQL 时间间隔

如何解决Clarion 中的 PostgreSQL 时间间隔

如何在 Clarion 中从 Postgresql 重写此查询？

select extract(epoch from (timestamp '02-01-2021 06:00' - timestamp '01-01-2021 22:00'))/3600 as interval_as_hours_numeric

解决方法

当您在 Clarion 中询问“如何重写 select extract(epoch from (timestamp '02-01-2021 06:00' - timestamp '01-01-2021 22:00'))/3600 as interval_as_hours_numeric”时，我假设您的意思是使用 Clarion 语法进行日期/时间数学运算。

如果您想通过 Clarion 文件驱动程序使用此查询并将其发送到 PostgreSQL，您可以使用以下代码：

mySQLtable{prop:SQL} = 'select extract(epoch from (timestamp <39>02-01-2021 06:00<39> - timestamp <39>01-01-2021 22:00<39>))/3600 as interval_as_hours_numeric'
NEXT(mySQLtable) 

结果将在 mySQLtable 记录结构的第一个字段中。

但是，我怀疑这不是您想要的，所以我将继续，就好像您想使用 Clarion 语法一样。我还将假设您对 Clarion 比较陌生，因此我可能会解释您已经知道的事情。

Clarion 没有时间戳数据类型。它支持日期和时间。它还通过使用 GROUP() 和 OVER() 组合 DATE 和 TIME 数据类型来间接支持 SQL DATETIME 类型。开发人员必须使用这种性质的策略来管理 DATE 和 TIME 的任何组合。因此，时间戳的日期和时间部分必须单独解析。

在 Clarion 中，您可以手动或通过 Clarion DEFORMAT() 动词解析日期和时间值。我在类方法中手动执行此操作，以便我不必担心将来 DEFORMAT 行为发生变化。为简单起见，我们将使用 DEFORMAT()。

还有其他（更好的）方法可以做到这一点，但这以解释的形式提供了您需要的东西，而不是可能无法解释为什么代码会这样做的更迟钝的类方法。

一些示例代码...

 PROGRAM

 MAP 
 END 

Time:Tick            EQUATE(1)
Time:Second          EQUATE(100 * Time:Tick)    ! there are 100 ticks in a second
Time:Minute          EQUATE(60 * Time:Second)
Time:Hour            EQUATE(60 * Time:Minute)
Time:Day             EQUATE(24 * Time:Hour)
Time:Midnight        EQUATE(1)                  ! timevariable=0 means "no time". timevariable=1 means midnight.
Time:FullDay         EQUATE(Time:Midnight + 23 * Time:Hour + 59 * Time:Minute + 59 * Time:Second + 99 * Time:Tick)
Time:AlsoFullDay     EQUATE(8640000)            ! the easy way to get 24 hours worth of Clarion time

strMyDate            STRING(10)
dMyDate              DATE  ! I tend to use LONGs for dates. Old habits,I guess. It doesn't really matter. 

strMyLaterDate       STRING(10) 
dMyLaterDate         DATE 

strMyTime            STRING(5)
tMyTime              TIME
intMyTime            LONG 

strMyLaterTime       STRING(5)
tMyLaterTime         TIME
intMyLaterTime       LONG 

intMyDate            LONG 
intDifferenceInHours LONG 

decDifferenceInHours DECIMAL(3,2)

intDifferenceInDays  LONG 

 CODE

 strMyDate = '01-01-2021'
 dMyDate = DEFORMAT(strMyDate,@D06-)  ! look in the help for "Date Pictures" to see why I used @D02. 

 ! at this point,dMyDate contains 01-01-2021 (Jan 1,2021) represented as a "Clarion Standard Date",which is the number of days elapsed since December 28,1800. 

 strMyLaterDate = '02-01-2021'
 dMyLaterDate = DEFORMAT(strMyLaterDate,@D06-) 

! at this point,dMyLaterDate contains 02-01-2021 (Jan 2,2021) represented as a Clarion Standard Date.


 strMyTime = '22:00'
 tMyTime = DEFORMAT(strMyTime,@T01)  ! look in the help for "Date Pictures" to see why I used @D02. 

 ! at this point,tMyTime contains 22:00 represented as a "Clarion Standard Time",which is the number of ticks since midnight. 
 ! A Clarion tick is 1/100th of a second. See the Time: equates above. 

 strMyLaterTime = '06:00'
 tMyLaterTime = DEFORMAT(strMyLaterTime,@T01) 

! at this point,tMyLaterTime contains 06:00 represented as a Clarion Standard Time. 

! Because there isn't a native datetime datatype in Clarion,we must do the math ourselves. This is a bit crude and not at all
! how I'd write this in a class,but I wanted it to function more as an explainer than as production code. 


! How do the dates match up?

 CASE dMyLaterDate - dMyDate
    OF -9999 to -1 ! dMyLaterDate is an earlier date than dMyDate 
       ! this code will be similar to the code below under "ELSE !dMyLaterDate is a later day than dMyDate"

    OF 0 ! same date,different times.

       IF tMyTime < tMyLaterTime 
          intDifferenceInHours = (tMyLaterTime - tMyTime) / Time:Hour
          decDifferenceInHours = (tMyLaterTime - tMyTime) / Time:Hour
       ELSIF tMyTime > tMyLaterTime 
           intDifferenceInHours = (tMyTime - tMyLaterTime) / Time:Hour
           decDifferenceInHours = (tMyTime - tMyLaterTime) / Time:Hour
       ELSE
          intDifferenceInHours = 0
          decDifferenceInHours = 0
       END 

   ELSE !dMyLaterDate is a later day than dMyDate (such as your example)
      intDifferenceInDays = dMyLaterDate - dMyDate
      intDifferenceInHours = Time:FullDay - tMyTime +        | ! partial day associated wth tMyDate,ie: from 22:00 to midnight
                             tMyLaterTime - Time:Midnight +  | ! partial day associated with tMyLaterDate,ie: from midnight to 06:00
                             (intDifferenceInDays - 1) * 24 * Time:Hour + 1  ! Difference in full days. The 1st day doesnt count (thus the -1),! as the times take care of that part of the difference.

     ! a little easier to read                            
     ! intDifferenceInHours = Time:FullDay - tMyTime + tMyLaterTime - Time:Midnight + (intDifferenceInDays - 1) * 24 * Time:Hour 

 END 
 
 MESSAGE('diff in hours=' & intDifferenceInHours / Time:Hour)
 
 RETURN