Using case when to insert values

问题

Below shows a executable statement: Successful attempt:

INSERT INTO Personnel_Assignment (DATE, testno, Hours) 
SELECT '21-OCT-2011', '12345', 
   CASE
      WHEN Extract(day From(S.ENDTIME-S.STARTTIME) ) >= 1 
         THEN (Extract(Day From(S.ENDTIME-S.STARTTIME) ) * 24 
            + Extract(Hour From(S.ENDTIME-S.STARTTIME) ) )
      WHEN S.endtime IS NULL
         THEN NULL
      ELSE
         Extract(Hour From(S.ENDTIME-S.STARTTIME) ) )
      ||'hrs' End ||
      Extract(Minute From(S.ENDTIME-S.STARTTIME) ) || 'Min' As Hours 
FROM Schedule S`

Please note that the data type for endtime and start time is timestamp with timezone in this format:

Nls_Timestamp_Tz_Format='HH24:MI TZR'

Just a question that i would like to ask: My datatype for hours is varchar2 And if i wish to sum my hours in the end from the results above, would it be tedious in converting it into number?

Thanks

回答1:

First of all, || Else doesn't make sense. The part after || has to be another expression to concatenate.

Secondly, you certainly can nest case expressions, but in your case you don't need to. A single case expression can have multiple when/then branches, in the form case when [condition_A] then [expression_if_A_is_true] when [condition_B] then [expression_if_A_is_false_and_B_is_true] else [expression_if_A_and_B_are_both_false] end.

来源：https://stackoverflow.com/questions/8176902/using-case-when-to-insert-values