What is query cost?

What is query cost?

• A. the time length of execution
• B. the number of rows returned
• C. the size of the result set in bytes
• D. the number of distinct values in a column

Answer: (A)

Query cost is the estimated resources needed to execute a query, used by the optimizer to compare different execution plans. It’s essentially a numeric measure that correlates with how long the query will take to run, accounting for CPU and I/O work. The optimizer uses this cost to pick the plan it expects will finish fastest or use the least resources. It’s not about how many rows are returned, the size of the result in bytes, or how many distinct values are in a column—that describes the output data, not the work to produce it. So the option describing the time length of execution best captures what query cost represents.

Query cost is the estimated resources needed to execute a query, used by the optimizer to compare different execution plans. It’s essentially a numeric measure that correlates with how long the query will take to run, accounting for CPU and I/O work. The optimizer uses this cost to pick the plan it expects will finish fastest or use the least resources. It’s not about how many rows are returned, the size of the result in bytes, or how many distinct values are in a column—that describes the output data, not the work to produce it. So the option describing the time length of execution best captures what query cost represents.