Is this query from Modern Database Management wrong?

Question

This is from the Modern Database Management text, chapter 12. Given:

Supplier_T(SupplierNumber,City)                10,000 records, stored in Detroit
Part_T(PartNumber, Color)                      100,000 records, stored in Chicago
Shipment_T(SupplierNumber, PartNumber)         1,000,000 records, stored in Detroit

A query written in SQL, is made to list the supplier numbers for Cleveland suppliers of red parts is given on page 19 is:

SELECT Supplier_T.SupplierNumber
FROM Supplier_T, Shipment_T, Part_T
WHERE Supplier_T.City = 'Cleveland'
AND Shipment_T.PartNumber = Part_T.PartNumber
AND Part_T.Color = 'Red';

But isn't it missing in the WHERE clause,

AND Supplier_T.SupplierNumber = Shipment_T.SupplierNumber

Maybe I'm just being too pedantic.

Answer 1

It might well be that the example is given in order to show what happens when one forgets to join between tables! This is called a Cartesian Join, and the result is that every row joins to every other row, producing a much much larger result set than one had expected.

I imagine that if the point of the query is to show red parts which are stored in Cleveland, then the query would be

SELECT Supplier_T.SupplierNumber
FROM Supplier_T
inner join Shipment_T on Shipment_T.suppliernumber = supplier_t.suppliernumber
inner join Part_T on Part_T.PartNumber = Shipment_T.PartNumber
WHERE Supplier_T.City = 'Cleveland'
AND Part_T.Color = 'Red';  

The fact that the query uses SQL-89 implicit join syntax (from table1, table2, table3) as opposed to SQL-92 explicit join syntax (from table1 inner join table2) should hint that something is wrong! What is written in the text after this query?