Question

I have table1 as below:

Col1    Bal
-------------------
 1       0
 2       0
 3       0
 4       0

Col1 is the key here.

I have table2 as below:

Col1    Bal    Date
---------------------
 1       5      x
 1       10     y
 1       7      z
 3       8      p
 3       9      m

Col1 is the join column in both tables.

I want to update bal in first table with sum of bal in 2nd table.

What would be the sql statement for this:

update table1 a set a.bal=(select sum(b.bal) from table2) where 

and I am lost!

After update, table1 should be:

Col1    Bal
-------------------
 1       22
 2       0
 3       17
 4       0

Answer 1

From the documentation, it looks like you can use table aliases in DB2:

update  table1 a 
set     bal = coalesce(
        (
        select  sum(b.bal) 
        from    table2 as b
        where   a.col1 = b.col1
        ), 0)