sql - LAG functions and NULLS -

how can tell lag function last "not null" value?

for example, see table bellow have few null values on column b , c. i'd fill nulls last non-null value. tried using lag function, so:

case when b null lag (b) on (order idx) else b end b, 

but doesn't quite work when have 2 or more nulls in row (see null value on column c row 3 - i'd 0.50 original).

any idea how can achieve that? (it doesn't have using lag function, other ideas welcome)

a few assumptions:

• the number of rows dynamic;
• the first value non-null;
• once have null, null end - want fill latest value.

thanks

if null way end can take short cut

declare @b varchar(20) = (select top 1 b table b not null order id desc); declare @c varchar(20) = (select top 1 c table c not null order id desc);  select is, isnull(b,@b) b, insull(c,@c) c  table;