Which of the following statements is wrong?Question 7Select one:a.Aggregate functions are mostly used in the WHERE clause of a SELECT statement.b.When using the equivalence operator (=) in the predicate, you must make sure that the subquery retrieves exactly one value.c.SQL's concept of joining two or more tables also applies to joining two copies of the same table.d.Output of the COUNT() function is the number of rows or column values that would be selected by the query.

To determine which statement is wrong, we need to analyze each option:

a. Aggregate functions are mostly used in the WHERE clause of a SELECT statement. This statement is incorrect. Aggregate functions, such as COUNT(), SUM(), AVG(), etc., are typically used in the SELECT clause to perform calculations on a set of rows and return a single value.

b. When using the equivalence operator (=) in the predicate, you must make sure that the subquery retrieves exactly one value. This statement is correct. When using the equivalence operator (=) in a subquery, it is important to ensure that the subquery returns exactly one value. Otherwise, it may result in an error or unexpected results.

c. SQL's concept of joining two or more tables also applies to joining two copies of the same table. This statement is correct. SQL allows you to join multiple tables together using the JOIN keyword. This concept also applies when joining two copies of the same table, which can be useful in certain scenarios.

d. Output of the COUNT() function is the number of rows or column values that would be selected by the query. This statement is correct. The COUNT() function in SQL returns the number of rows or column values that would be selected by the query. It is commonly used to count the number of records in a table or the number of occurrences of a specific value.

Therefore, the incorrect statement is option a. Aggregate functions are not mostly used in the WHERE clause of a SELECT statement.