Question 6: (1.00) One of the main rules that subqueries must follow: Subqueries must be enclosed within parentheses Subquery can have multiple columns in the SELECT clause Subqueries that return more than one row can only be used with multiple value operators, such as the >, <,=, >=, <= A subquery can return zero or more rows The BETWEEN operator can be used with a subquery

The text appears to be a list of rules that subqueries in SQL must follow. Here's a step-by-step explanation:

1. "Subqueries must be enclosed within parentheses": This means that whenever you write a subquery, it must be enclosed within parentheses. For example: SELECT * FROM table WHERE id IN (SELECT id FROM another_table).

2. "Subquery can have multiple columns in the SELECT clause": This means that a subquery can select more than one column. For example: SELECT id, name FROM table WHERE id IN (SELECT id FROM another_table).

3. "Subqueries that return more than one row can only be used with multiple value operators, such as the >, <,=, >=, <=": This means that if a subquery returns more than one row, it can only be used with operators that can handle multiple values. For example, you can't use the = operator with a subquery that returns more than one row.

4. "A subquery can return zero or more rows": This means that it's possible for a subquery to return no rows at all. This might happen if the condition in the WHERE clause of the subquery isn't met.

5. "The BETWEEN operator can be used with a subquery": This means that you can use the BETWEEN operator in the WHERE clause of a subquery. For example: SELECT * FROM table WHERE id BETWEEN (SELECT MIN(id) FROM another_table) AND (SELECT MAX(id) FROM another_table).