SQL command to select first record

Question

I would like to create an SQL command to link two tables on a field so that only the first matching record is selected. What would be the syntax for that? Thank you.

Answer 1

Actually, that's not as simple as it sounds...  It also depends on your definition of "first", and what data you are looking for.
For example, if you are looking for the earliest order date for each of your customers, you could do something like:
select customer.code, customer.name, min(order.date) as First_Order_Date
from customer, order
where customer.code = order.cust_code
group by customer.code, customer.name
But if you also want the sales dollars for that first order, you'd have to do something like:
select customer.*, firstOrder.first_order_date, sales.sales
from customer
join (
  select cust_code, min(date) as first_order_date
  from order
  group by cust_code
) firstOrder
on customer.code = firstOrder.cust_code
join (
  select cust_code, date, sum(sales) as sales
  from order_detail
  group by cust_code, date
) sales
on firstOrder.cust_code = sales.cust_code and firstOrder.First_Order_Date = sales.date
HTH,
Carl