Rule Definition
A query that retrieves all columns of a table can potentially be the source of important changeability problems. One cannot control how the columns will be ordered and returned to the client. This can lead to important data inconsistencies and thus stability issues. Also performance problems may arise when the execution of the query returns a large result sets (many row with all the columns may then become a huge amount of data to transport over the network). Thus optimizer module can't provide a correct execution.

Remediation
Review the design of the query to select only useful columns. For EF, this is achieved thanks to a LINQ Select clause: by using eager loading with the Include method, we reduce the number of database roundtrips, resulting in a significant improvement in query execution time.

Violation Code Sample

using System.Linq;
using YourDbContextNamespace;

public class YourProgramClass
{
    public static void Main(string[] args)
    {
        using (var context = new YourDbContextClass())
        {
            foreach (var blog in context.Blogs) // ⚠️ VIOLATION : Retrieve all columns of all blogs
                Console.WriteLine("Blog: " + blog.Url);
            }
        }
    }
}

sample 2

var customer =
 (from cust in dataContext.Customers    // ⚠️ VIOLATION : all columns are retrieved
 select cust).ToList();

Fixed Code Sample

using System.Linq;
using YourDbContextNamespace;

public class YourProgramClass
{
    public static void Main(string[] args)
    {
        using (var context = new YourDbContextClass())
        {
            foreach (var url in context.Blogs.Select(b => b.Url)) // ✓ FIXED: Retrieve only the Url column
            {
                Console.WriteLine("Blog URL: " + url);
            }
        }
    }
}

sample 2

var customer =
 (from cust in dataContext.Customers
 select new {                             // ✓ FIXED : only 3 named columns are retrieved
 customer. CustomerID,
 customer.Name,
 customer.Address
 }). ToList ();

Microsft Entity Framework - Efficient Querying - Project only properties you need https://learn.microsoft.com/en-us/ef/core/performance/efficient-querying#project-only-properties-you-need Optimizing database performance in Entity Framework https://www.site24x7.com/learn/optimize-entity-framework-performance.html