What does the 'filtered' column in an explain statement represent?

The 'filtered' column in an explain statement indicates the percentage of rows that were excluded from the result set during the query process. This information is valuable because it shows how effective any filtering conditions, such as WHERE clauses or JOIN conditions, are at reducing the number of rows examined to find the desired results.

By understanding how many rows are filtered, developers can optimize their queries to make them more efficient. A high percentage in the 'filtered' column may suggest that the WHERE clause or other restrictions are significantly narrowing down the dataset, which is often a positive indicator of query performance. This column allows developers to assess and refine their queries based on how much data is being filtered out, thus leading to improved database performance and reduced processing time.