Question

 insert into tableA (column1) 
 select min(tableC.column1)
 from tableB 
 inner join tableC on (tableC.coumn2 = tableB.column1
 and tableB.column2 = tableA.column2) 
 group by tableA.column2

How would I change the above to a update with group by instead of insert with group by based on the criteria tableB.column2 = tableA.column2 ?

Note that I am using SQL SERVER 2008.

Answer 1

  Update A set Column1 = minC    
    from (select Ab.Column2, min(C.Column1) as minC
            from A Ab
            inner join B on Ab.Column2 = B.Column2
            inner join C on C.column2 = B.Column2 --No need to add again the A.col2 = B.col2
            group by Ab.Column2) Grouped where A.Column2 = Grouped.Column2

Is this what you want?
This will get for each columnA the C.Column1 min value, and will update it in A.Column1 (that’s where you were inserting before), based on condition A.Column2 = Grouped.Column2.

here is a SQL-Fiddle Demo