What must you do to create an analytical store in an existing Azure Cosmos DB container?

To create an analytical store in an existing Azure Cosmos DB container, enabling Azure Synapse Link on the container is essential. Azure Synapse Link allows you to connect your Azure Cosmos DB data to Azure Synapse Analytics, facilitating real-time analytics without the need to create a separate copy of the data. This process effectively creates a dedicated analytical store that can be queried using powerful analytical capabilities.

Once Azure Synapse Link is enabled, the existing data in the container becomes available for analytical workloads within Azure Synapse, enabling you to perform complex queries and analysis without disrupting the performance of your transactional operations. This feature is particularly beneficial for organizations looking to derive insights from their operational data while maintaining a cohesive synchronization between transactional and analytical processes.

The other options do not relate directly to the creation of the analytical store. Adding a new item to the container, changing the partition key strategy, and scaling the throughput may be necessary for different operational purposes but are not prerequisites for creating an analytical store using Azure Synapse Link. The primary function of Synapse Link is to bridge the gap between operational data and analytical processes, making it the correct action for this scenario.