SQL中总和的差异

Question

I have a table like the following:

PARENTREF    TRANSTYPE(BIT(1))    DUEDATE(DateTime)    TOTAL
     2038                    0           2015-01-01     1000
     2038                    1           2015-03-05      500
     2039                    0           2015-01-01     1000
     2040                    0           2015-01-01     1000
     2041                    0           2015-01-01     1000
     2040                    1           2015-04-07      200

I want a SELECT query that returns SUM(TOTAL) when TRANSTYPE=1 subtracted from SUM(TOTAL) when TRANSTYPE=0 for each distinct PARENTREF . I also would like to get in a separate column the DUEDATE for the PARENTREF when TRANSTYPE=0 . There may be only one PARENTREF with TRANSTYPE=0 so that won't be a problem. In other words, I should get the following table:

PARENTREF    DUEDATE(DateTime)    TOTAL
     2038          2015-01-01       500
     2039          2015-01-01      1000
     2040          2015-01-01       800
     2041          2015-01-01      1000

Answer 1

(1-transtype*2) is 1 when transtype=0 and is -1 when transtype=1 , so query subtract values of total where transtype=1 from value of total where transtype=0 . max ignore null values, so it select only not null value where transtype=0 .

select
    parentref,
    sum((1-transtype*2)*total) as total,
    max(if(transtype=0,duedate,null)) as duedate
from tablename
group by parentref

Answer 2

Try this....

select t.PARENTREF,t.DueDate,(t.Total-isnull(m.Total,0)) as total 

   from tabl t LEFT outer join tabl m on t.PARENTREF=m.PARENTREF and t.TRANSTYPE <> m.TRANSTYPE

   where (t.Transtype=0 ) and (isnull(m.Transtype,1)=1 )

Please Check out this fiddle http://sqlfiddle.com/#!3/d4988/1

or use thiss...

  select t.PARENTREF,t.DueDate,(sum(t.Total)-sum(isnull(m.Total,0))) as total 
   from tabl t LEFT outer join tabl m on t.PARENTREF=m.PARENTREF and t.TRANSTYPE <> m.TRANSTYPE
   where (t.Transtype=0 ) and (isnull(m.Transtype,1)=1 )
   group by t.PARENTREF,t.DueDate

Check this fiddle http://sqlfiddle.com/#!3/d4988/2