In SQL, the SELECT statement retrieves data from one or more tables in a database. It allows you to specify which columns to retrieve and may include conditions to filter rows. The fundamental purpose of the SELECT statement is to fetch data from the database tables.

The correct option is Where and Select. You would use the Where operator to filter the products that are in stock and have a price greater than $50, and then use the Select operator to project the results into a new collection containing only the required product information. This combination allows you to filter and select the desired products in a single query.

Monitoring the number of connections in use and the connection wait time is essential to understand the current utilization of the connection pool and identify any potential bottlenecks. By adjusting the pool size settings, such as "Max Pool Size" and "Min Pool Size," and evaluating parameters like "Connection Lifetime," you can optimize the connection pool for better performance.

In scenarios where multiple users are modifying the same data concurrently, concurrency control mechanisms such as locking can help ensure data integrity by preventing conflicting modifications from occurring simultaneously.

The [Key] attribute in Entity Framework is commonly applied to specify the identity property of an entity, indicating the property that uniquely identifies each instance of the entity.

Entity Framework (EF) stands for Entity Framework. It is an Object-Relational Mapping (ORM) tool provided by ADO.NET, facilitating developers to work with relational data as domain-specific objects, eliminating the need for most of the data access plumbing code.

In an INSERT command in SQL, the VALUES clause is used to specify the values to be inserted into the specified columns of a table. It allows you to define the data that will be added to the table.

Eager loading retrieves all related data at once, which can enhance performance by reducing the number of database calls. This is done using the LoadWith method of DataLoadOptions.

To optimize LINQ queries for performance, you can use the AsQueryable method to reduce the number of database calls. This method converts an IEnumerable collection to an IQueryable collection, allowing the query to be executed on the database server instead of in-memory. This can lead to significant performance improvements, especially when dealing with large datasets or complex queries.

In DataGrid or DataGridView controls, you can enable data editing by setting the "EditMode" property to allow users to edit the data displayed in the control.

The use of stored procedures can help improve performance and security in database applications. By precompiling SQL statements, stored procedures reduce the overhead of repeated compilation, leading to better performance. Furthermore, they enhance security by allowing controlled access to database objects and minimizing the risk of SQL injection attacks.

Optimistic concurrency is the preferred model for handling potential conflicts when multiple users can update the same record simultaneously. It assumes that conflicts are rare, allowing multiple users to access and modify the data concurrently. When a user attempts to commit changes, the system checks whether the data has been modified since it was last retrieved. If no modifications are detected, the changes are applied successfully.