Which statement best explains the benefit of filtering data at the reader stage using a WHERE clause rather than filtering after reading with a Tester?

Which statement best explains the benefit of filtering data at the reader stage using a WHERE clause rather than filtering after reading with a Tester?

• A. It reduces unnecessary data I/O by not reading filtered data.
• B. It reads data and then filters, which can be slower.
• C. It is compatible with all databases.
• D. It eliminates the need to set any filter.

Answer: (A)

Filtering at the reader stage using a WHERE clause means the data source applies the condition as it retrieves rows, so only matching records are read. This minimizes data movement and memory use because unnecessary features never enter the workspace. In many databases, the WHERE clause can use indexes, speeding up retrieval further. If you read everything and then filter with a Tester, every feature is loaded into the workspace first, even those that will be discarded, causing more I/O and CPU work and slowing things down—especially with large datasets. Filtering early saves resources and speeds up processing, which is why it’s the best approach.

Filtering at the reader stage using a WHERE clause means the data source applies the condition as it retrieves rows, so only matching records are read. This minimizes data movement and memory use because unnecessary features never enter the workspace. In many databases, the WHERE clause can use indexes, speeding up retrieval further.

If you read everything and then filter with a Tester, every feature is loaded into the workspace first, even those that will be discarded, causing more I/O and CPU work and slowing things down—especially with large datasets. Filtering early saves resources and speeds up processing, which is why it’s the best approach.