Correlated subquery in SQL

Question

I have two tables: Table A and Table B

1. Table A and Table B both have RowId column.
2. Table A and Table B both have ModifiedAt col

Answer 1

DECLARE @RowId INT

DECLARE CurRowId CURSOR FOR SELECT RowId FROM Patients

OPEN CurRowId

FETCH NEXT FROM CurRowId INTO @RowId

WHILE @@FETCH_STATUS = 0

BEGIN

if not exists (select * from dbo.ResultsStored where ModifiedAt >

                 (select ModifiedAt from dbo.Patients where RowId = 
                                                                   @RowId))

begin

print'not exists'

end

else

begin

print 'exists'

END

FETCH  NEXT FROM CurRowId INTO @RowId

END

Answer 2

The problem is in your data. If I understand correctly you want to know if there are such rows in Results which date is greater then Patients date. If no such row is found then it is OK.

If so your query looks correct. You can directly select incorrect data by:

SELECT  *
FROM    Patients p
        CROSS APPLY ( SELECT    MAX(ModifiedAt) AS ModifiedAt
                      FROM      ResultsStored rs
                      WHERE     p.RowId = rs.RowId
                    ) a
WHERE   a.ModifiedAt > p.ModifiedAt