Which chart shows the average number of running SQL statements historically?

The chart that shows the average number of running SQL statements historically is one that specifically tracks the count of SQL statements that are actively executing at any given time. This option directly correlates with monitoring and assessing the database's performance by evaluating how many statements are currently running, which can be crucial for database optimization and resource allocation.

Monitoring the running SQL statements provides insights into potential bottlenecks or performance issues since a high number of concurrent SQL executions could indicate heavy load or inefficient queries. This historical view is essential for understanding how workloads change over time and allows database administrators to make informed decisions about necessary adjustments or optimizations.

In contrast, the other options focus on different aspects of SQL performance or behavior. For instance, tracking queued statements would relate to SQL statements that are waiting to run, while average SQL statement response time measures how long it takes for statements to execute rather than focusing solely on how many are running at any one time. Similarly, the metric of SQL statements executed per second reflects performance in terms of throughput but does not provide a historical record of the number of currently executing SQL statements, which is what the correct chart specifically captures.