Conditional filtering allows you to apply different criteria to rows in a table depending on certain conditions. This is especially useful when you want to filter results flexibly based on column values. The CASE WHEN expression in SQL can be used within a WHERE clause to create such dynamic filtering logic. By using CASE WHEN, you can apply different filtering thresholds or rules based on the data in each row, rather than being restricted to a single condition for all rows. This technique is powerful when you need to handle complex business logic directly in your queries.

In the query above, CASE WHEN is used inside the WHERE clause to apply different rating thresholds depending on the movie's genre. For "Action" movies, only those with a rating of at least 8.5 are selected. For "Drama" movies, the threshold is even higher at 9.0. All other genres must have a rating of at least 8.0 to be included. The CASE WHEN expression evaluates each row, and the result of the expression determines whether the row passes the filter. If the condition in the CASE block evaluates to true, the row is included in the result set. This approach allows you to implement advanced filtering logic without writing multiple queries or using complex OR and AND combinations.