Extracting and interpreting data can be very valuable to an organization.
Describe the importance of using sub queries in a database system. Provide at least two business case scenarios to support your response.
Advanced SQL and PL/SQL
Sample Answer
Using subqueries in a database system is important for performing complex data extraction and analysis. A subquery, also known as an inner query or nested query, is a query embedded inside another SQL query. They allow you to use the results of one query as a condition for another, enabling multi-step operations in a single statement. .
Importance of Subqueries
Subqueries are crucial for several reasons:
Complex Filtering: They enable filtering data based on values that are the result of another aggregate function or calculation. For instance, you can find all customers who have placed an order with a total value greater than the average order value across all customers. This type of filtering is impossible with a single WHERE clause alone.
Dynamic Conditions: Subqueries provide dynamic conditions. The inner query is executed first, and its result is then used by the outer query. This makes the query flexible and eliminates the need for manual, hard-coded values that may change over time.
Improved Readability: In many cases, a subquery can make a complex query more readable and easier to understand than a lengthy join. By breaking down the logic into smaller, more manageable parts, a developer can clearly see what the query is trying to accomplish.
Data Aggregation and Comparison: They allow you to compare a single value or a list of values to a set of data. This is particularly useful for finding records that do not exist in another table or for identifying outliers.