The correct answer is "JoinLeft". In LINQ, to perform a left outer join, you need to use the Join method along with the DefaultIfEmpty method. This combination allows you to include results from the left side of the join even if there are no matches on the right side.

LINQ queries with lambda expressions and aggregations are often preferred in scenarios involving filtering and aggregating data from multiple sources due to their concise syntax and ability to handle complex logic effectively. Lambda expressions provide flexibility in defining custom conditions and aggregations, making them suitable for diverse data manipulation tasks.

The correct answer is "GroupBy". The GroupBy method in LINQ is used to group query results based on a specified key. It allows you to perform operations on each group separately, such as aggregation or filtering. This is commonly used for grouping data in LINQ queries.

The correct answer is "Sum". In LINQ, the Sum extension method is used for aggregating numeric data. It calculates the sum of all the values in a collection or the sum of a specific property of elements in the collection. This is commonly used for calculating totals or subtotals.

Writing efficient LINQ queries involves minimizing unnecessary data retrieval from the database. Projections allow you to select only the required fields, reducing the amount of data transferred over the network and improving query performance. By fetching only essential data, you can optimize resource utilization and minimize database load, especially in scenarios with complex data models.

Projection queries in Entity Framework allow for selecting only the necessary fields from the database, resulting in reduced data transfer between the database and the application. This reduction in data transfer leads to improved query execution time and enhanced memory utilization, ultimately optimizing database access for better performance.

LINQ's Select method enables the transformation of query results into a custom data structure by specifying the desired fields or properties. By projecting query results, you can shape the output according to the requirements, facilitating seamless integration with downstream processing or presentation layers. This approach enhances code readability and maintainability by encapsulating the data transformation logic within the LINQ query.

A projection query in Entity Framework involves selecting specific columns from a table rather than retrieving all columns. It helps in reducing data transfer and can improve performance, especially when dealing with large datasets.

In LINQ and Entity Framework, the Select method is commonly used to specify which columns to retrieve from a table. It allows developers to project only the required data, leading to more efficient queries and reduced overhead.

The Select method in LINQ is commonly used for transforming the results of a query into a different shape. It allows developers to project the elements of a sequence into a new form, such as selecting specific properties or performing calculations.