Filling Up Missing Columns Data

Hi,

I have the following table :




Code Block
Create table #Customers (custid int,name nvarchar(20),age int, st_code int,
citycode int, internalid int,type int,oldcustid int)

Insert into #Customers values(101,'Aron',23,1,1,12,1,0);
Insert into #Customers values(102,'Cathy',28,1,1,13,1,0);
Insert into #Customers values(103,'Zarog',33,1,1,14,1,0);
Insert into #Customers values(104,'Michale',25,1,2,12,1,0);
Insert into #Customers values(105,'Linda',43,1,2,13,1,0);





Insert into #Customers values(106,'Burt',53,1,2,14,1,0);


If you observe, the rows are unique based on the internalid per st_code,per city_code

Problem :
Now the user inserts another row but this time he passes only the following :

Insert into #Customer values(120,'AronNew',null,1,1,12,null,null) -
Note he doesnt pass the age or the type

I want that when he passes this row, i match up this row with the existing row based on st_code,citycode and internalid and then update the new row with the missing values(only columns with null) that were there in the existing row

OUTPUT

120,'AronNew',23,1,1,12,1,0

How could I write the query for this?

thanks.