Consider the numbers of rows for the city and country tables.
mysql> SELECT COUNT FROM City;
How many rows will the following query produce?
SELECT * FROM City, Country
A.
0
B.
1
C.
4079
D.
4318 (the sum of 239 and 4079)
E.
974881 (the product of 239 and 4079)
F.
None of the above; the query will produce a syntax error.
Explanation:
Comma Join with no WHERE CLAUSE will result in a Cartesian Produce Join and multiply no of rows in city by no of rows in county.