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Editorial Team
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Asked: 2026-06-05T12:56:32+00:00

Assume we have a table called Persons and another table called Product_Orders. We will

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Assume we have a table called “Persons” and another table called “Product_Orders”. We will give the table aliases of “p” and “po” respectively.

Now we want to list all the orders that “Ola Hansen” is responsible for.

We use the following SELECT statement:

SELECT po.OrderID, p.LastName, p.FirstName 
FROM Persons AS p, Product_Orders AS po 
WHERE p.LastName='Hansen' AND p.FirstName='Ola'

Im confused with the OrderID, becouse it is not compared to anything such like.

SELECT po.OrderID, p.LastName, p.FirstName 
FROM Persons AS p, Product_Orders AS po 
WHERE p.LastName='Hansen' AND p.FirstName='Ola'
  AND po.OrderID = p.OrderID.

Am I wrong?

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1 Answer

  1. Editorial Team

    You are right, in your first query, each row from the first table is joined with each row from the second one. Which will result in a result for each order (ignoring whether or not the order belongs to Ola Hansen).

    However, I doubt that your table Persons contains forreign keys to orders. A clause such as

    SELECT po.OrderID, p.LastName, p.FirstName 
FROM Persons AS p, Product_Orders AS po 
WHERE p.LastName='Hansen' AND p.FirstName='Ola'
AND po.PersonID = p.PersonID

    would be more sensible, assuming that each row in the Product_Orderds contains a forreign key to the Person that did the order.

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