IF else condition on DATE to determine String in other column
i didn't understood what you are meaning with "NEW = 'CHANGE', OLD = 'NO CHANGE' like you will ..." so i wrote 2 cases

Assuming that DataColumn and StrnigColumn are the columns names and myTable is the table name

you have to use a CASE with the DATEADD function 

UPDATE myTable
SET StringColumn = CASE WHEN DATEADD(DAY,GETDATE(), -3) &gt; DateColumn 
                        THEN 'NO CHANGE' 
                        ELSE 'CHANGE'
                   END


if you mean by "NEW = 'CHANGE', OLD = 'NO CHANGE' like you will ..." that you have also to check the value so your query will look like

UPDATE myTable
SET StringColumn = CASE WHEN DATEADD(DAY,GETDATE(), -3) &gt; DateColumn AND StringColumn ='OLD'
                                            THEN 'NO CHANGE' 
                        WHEN DATEADD(DAY,GETDATE(), -3) &lt;= DateColumn AND StringColumn ='NEW'
                                            THEN 'CHANGE'
                        ELSE [StringColumn]
                   END