Ok, so I got my SAS Certification Prep Guide for Advanced Programming today and went over the first chapter. I also did the quiz at the end. But there is one question in particular that still confuses me.

Here it is:

Which statement is true regarding the use of the PROC SQL step to query data that is stored in two or more tables?

a) When you join multiple tables, the tables must contain a common column.
b) You must specify the table from which you want each column to be read.
c) The tables that are being joined must be from the same type of data source.
d) If two tables that are being joined contain a same-named column, then you must specify the table from which you want the column to be read.

The correct answer is (d), but isn't (a) also correct? What's wrong with (a)?

a) When you join multiple tables, the tables must contain a common column.
but isn't (a) also correct? What's wrong with (a)?

condition a) is not necessary to join the tables. Because if there is no common column between the tables, still we can do join. It will be cross product of the tables.