Question

I have two tables :

create table CurrentDay (
ID int identity primary key,
ssn varchar(10), 
val money, 
CheckDate datetime, 
CurrentStatus tinyint)

create table PreviousDay (
ID int identity primary key,
ssn varchar(10), 
val money, 
CheckDate datetime, 
CurrentStatus tinyint)

I need update field CurrentDay.CurrentStatus with this values:

• 111,if in the PreviousDay.ssn is the same ssn as in the CurrentDay and if the PreviousDay’s val is the same as in the CurrentDay;
• 112,if in the PreviousDay.ssn is the same as in the CurrentDay and if the PreviousDay’s val is bigger as in the CurrentDay;
• 113,if in the PreviousDay.ssn is the same as in the CurrentDay and if the PreviousDay’s val is smaller as in the CurrentDay;
• 114,if in there is not PreviousDay.ssn the same as in the CurrentDay i.e. the ssn in CurrentDay only (it is today’s info) .

I’d wrote some query,but i it is desirable to find other way for doing this task using only one join between PreviousDay and CurrentDay tables. Obviously,that this isn’t a very lucky kind…Here is my variant:

Update CurrentDay 
Set CurrentStatus=case
when exists (select PreviousDay.ID from PreviousDay 
where PreviousDay.ssn=CurrentDay.ssn AND 
PreviousDay.val=CurrentDay.val  AND
PreviousDay.CheckDate=DATEADD(day,-1,CurrentDay.CheckDate))
then 111
when exists (select PreviousDay.ID from PreviousDay 
where PreviousDay.ssn=CurrentDay.ssn AND 
PreviousDay.val>CurrentDay.val  AND
PreviousDay.CheckDate=DATEADD(day,-1,CurrentDay.CheckDate))
then 112
when exists (select PreviousDay.ID from PreviousDay 
where PreviousDay.ssn=CurrentDay.ssn AND 
PreviousDay.val<CurrentDay.val  AND
PreviousDay.CheckDate=DATEADD(day,-1,CurrentDay.CheckDate))
then 113
when exists (select PreviousDay.ID from PreviousDay 
where PreviousDay.ssn!=CurrentDay.ssn AND 
PreviousDay.CheckDate=DATEADD(day,-1,CurrentDay.CheckDate))
then 114
end;

Here is other query,but in that case i cannot update CurrentDay.CurrentStatus’ fieid with value 114 because there is only matching rows on ssn in both tables:

Set Currentday.CurrentStatus=(select 111 where PreviousDay.val=CurrentDay.val union all select 112 where and PreviousDay.val>CurrentDay.val
union all select 113 where and PreviousDay.val<CurrentDay.val /*union all select 114 */ )
from PreviousDay join CurrentDay on PreviousDay.ssn=CurrentDay.ssn and PreviousDay.CheckDate=DATEADD(day,-1,CurrentDay.CheckDate)

Do you have any other ideas?

Answer 1

Something like:

UPDATE
    C
Set
    CurrentStatus = CASE
            WHEN P.val = C.val THEN 111
            WHEN P.val > C.val THEN 112
            WHEN P.val < C.val THEN 113
            ELSE 114 ---this works because if P.VAL is null, that is no matching row
        END
FROM
    CurrentDay C
    LEFT JOIN
    PreviousDay P On C.ssn = P.ssn AND P.CheckDate = DATEADD(day, -1, C.CheckDate))