In database management, a Cartesian product, also known as a cross join, is the result of combining rows from two or more tables by matching all rows from the first table with all rows from the second table. This can result in a large number of unnecessary rows in the output, especially when the tables involved are large. A merge join is a more efficient way to combine rows from two tables, as it only matches rows that have the same value in a common column.
To avoid a Cartesian product in a merge join, you can use the ON clause in the JOIN statement to specify the common column that should be used for matching rows. For example, the following SQL statement uses the ON clause to specify that the id column in the customers table should be matched with the id column in the orders table:
