I have an existing database and I want to change it so that if no value is
inserted into a column that it populates that column with a zero instead of a
null value. How do I make this change? I suspect I need to change all the
existing nulls to zero before making the change? Any help would be greatly
appreciated.

That depends.  Are you happy with the existing nulls?  If so, simply add a
default constraint:

alter table MyTable
add
    constraint DF1_MyTable default (0) for MyColumn

However, if you need to keep all nulls out, then populate the null columns
with some value and then alter the column:

alter table MyTable
alter column
    MyColumn int not null
go

Then, add the default constraint as shown above.

I have an existing database and I want to change it so that if no value is
inserted into a column that it populates that column with a zero instead of
a
null value. How do I make this change? I suspect I need to change all the
existing nulls to zero before making the change? Any help would be greatly
appreciated.

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