Equijoins:
An equijoin is a type of join operation that uses the equality operator to match rows between two tables based on a common column. It performs a comparison between the values of the specified columns in the two tables and returns the rows where the values are equal. The equality operator used in equijoins is typically the "=" operator.

Cartesian Join:
A Cartesian join, also known as a Cartesian product, is a join operation that combines each row from one table with every row from another table. It does not require any specific condition or operator to match the rows between the tables. Instead, it results in a combination of all possible pairs of rows from both tables, resulting in a large result set.

Join Condition with Equality Operator:
To perform a join operation, a join condition is required to specify how the rows from the two tables should be matched. This condition typically includes an equality operator to compare the values of a specific column in both tables.

Answer Explanation:
The question asks which join condition contains an equality operator.
- Option A: Equijoins specifically use the equality operator to match rows based on a common column. Therefore, the join condition in equijoins contains an equality operator.
- Option B: Cartesian joins do not require a specific condition or operator to match rows. Instead, they combine all possible pairs of rows from both tables.
- Option C: The correct answer is option A because equijoins use the equality operator, while Cartesian joins do not have a specific join condition.
- Option D: None of the mentioned is incorrect because equijoins do contain an equality operator in the join condition.

In summary, the join condition that contains an equality operator is an equijoin, making option A the correct answer.