I have placed the relevant parts of the documentation in a separate document. SAS SQL Documentation You are asking why the constraint: us.Capital = c.City is necessary in the where statement. I will turn this around and ask you to look at what you get if you do not include it. You will get all rows where this is true: us.Name = pc.Name and pc.Code = c.State; We have not required that only the capital cities are used. As written we will take all the cities found in the C table. While a city in the C table may not be a state capital, it will still match with the US table by the state. For example the city of Anchorage is found in table C. This select statement will include a row for Anchorage with the state name, the appropriate Postal Code for that state, and its coordinates. It would have a blank for the capital, the first column in the report.
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