multi restaurant online ordering system

You don't. Don't even think about using one row - it won;t work well, because you have no idea how many items any customer might order.

Suppose you say "nobody is going to order more than 40 items". What happens when they do?
And, what if Taylor also puts in an order for his mother, at the next table?
Instead, use a number of database tables.
One table holds info on the customer, and has a primary key which is the customer ID - this can include the password hash, the user name, and where he is.
A second holds customer orders - this had a primary key which is the order number, and a foreign key which is the customer, and a datetime which is when it was placed, and "completed", "paid" and "total" columns if you need them (and you probably do)
A third table holds the items he can order: primary key is an ItemID, it also holds the price, and the number you can serve (so you can remove items when the kitchen "runs out")
A fourth table holds order details: Primary key is an OrderItemID (but this is just a unique value to the table), with foreign keys to the Orders table, Items table and a "number of items ordered" column.

Sounds complicated? Yes, a bit - but it's a lot, lot simpler than trying to faff about with just one table, trust me!

Try it on paper with a pencil - you'll see what I mean!