create table clients
(
    client_id int not null identity(1,1) primary key nonclustered,
    user_name nvarchar(256) not null check (len(user_name) > 0) unique clustered,
    password varbinary(256) not null
)

create table products
(
    product_id int not null identity(1,1) primary key nonclustered,
    client_id int null references clients(client_id),
    name nvarcahr(256) not null check (len(name) > 0),
    description nvarchar(1024) null,
    unit_price money not null default 0.0000,
    enabled bit not null default (0),
    date_created datetime not null default current_timestamp
)

create table client_products
(
    client_product_id int not null identity(1,1) primary key nonclustered,
    client_id int not null references clients(client_id),
    product_id int null,
    name nvarchar(256) not null check (len(name) > 0),
    description nvarchar(1024) null,
    unit_price money not null default 0.0000
)

create trigger client_products_to_products on client_products for insert
    begin
        insert into products (client_id, name, description, unit_price, enabled)
            select client_id,
                   name,
                   description,
                   unit_price,
                   0
              from inserted
    end

quote:

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1) Clients can add products to their table from the master table, but they don’t have to — they can add products manually if they wish.

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