Set SQL column in table A based on column in table B

Question

I just can't quite get this syntax correct. Table 'clients' has a points_per_month column. Table 'usage' has an 'available' column and a 'client_id' column. I basically want to rewrite the available value to match the points_per_month value. I tried this:

update usage
set available = c.points_per_month
from usage u
inner join clients c on u.client_id = c.ident;

But that's setting all of the available values to the exact same number (the points_per_month of the first client returned)

Answer 1

Try something like

update usage u
set available = c.points_per_month
from clients c 
where u.client_id = c.ident;

Answer 2

The classic way with a subselect as assignment should work for every database:

update usage
set available = (select c.points_per_month
                   from clients c
                  where usage.client_id = c.ident
);