Question

A non-co-related subquery is executed only once and then its result used for all tuples of the outer query.

Option 1: Co-related Subquery
Option 2: Non-co-related Subquery
Option 3: Nested Subquery
Option 4: Aggregate Subquery

Answer 1

A non-co-related subquery is executed once and then its result is applied to the outer query in SQL, differing from a co-related subquery which executes multiple times based on the outer query's rows.

Step-by-step explanation:

A Non-co-related Subquery is a type of subquery in SQL queries where the inner query is executed once and its result is used to evaluate the outer query. This is in contrast to a co-related subquery where the inner query may be executed multiple times, depending on the number of rows evaluated in the outer query. Non-co-related subqueries are useful when you need a single value or a set of values to compare against all rows selected by the outer query.

An example of such a subquery would be selecting all customers from a database who have made purchases greater than the average purchase amount. The subquery to find the average purchase is only run once, and then its result is used in the comparison for each customer.