Fix ORDER BY type comparison with custom comparer

Co-authored-by: MPCoreDeveloper <37024522+MPCoreDeveloper@users.noreply.github.com>

Author: Copilot

SharpCoreDB.Tests/IndexTests.cs

@@ -197,7 +197,7 @@ public void HashIndex_UpdateOperations_MaintainConsistency()
 
         // Act - Update status
         var updatedRow = new Dictionary<string, object> { { "id", 1 }, { "status", "inactive" }, { "name", "Item1" } };
-        index.Remove(rows[0]);
+        index.Remove(rows[0], 0);
         index.Add(updatedRow, 0);
 
         // Assert - Index should reflect changes

SharpCoreDB/DataStructures/Table.cs

@@ -228,10 +228,35 @@ private List<Dictionary<string, object>> SelectInternal(string? where, string? o
         {
             var idx = this.Columns.IndexOf(orderBy);
             if (idx >= 0)
-                results = asc ? results.OrderBy(r => r[this.Columns[idx]]).ToList() : results.OrderByDescending(r => r[this.Columns[idx]]).ToList();
+            {
+                var columnName = this.Columns[idx];
+                // Use Comparer<object>.Default which handles type mismatches gracefully
+                results = asc 
+                    ? results.OrderBy(r => r[columnName], Comparer<object>.Create((a, b) => CompareObjects(a, b))).ToList()
+                    : results.OrderByDescending(r => r[columnName], Comparer<object>.Create((a, b) => CompareObjects(a, b))).ToList();
+            }
         }
         return results;
     }
+    
+    private static int CompareObjects(object? a, object? b)
+    {
+        // Handle nulls
+        if (a == null && b == null) return 0;
+        if (a == null) return -1;
+        if (b == null) return 1;
+        
+        // If same type, use default comparison
+        if (a.GetType() == b.GetType())
+        {
+            if (a is IComparable ca)
+                return ca.CompareTo(b);
+            return 0;
+        }
+        
+        // Different types - compare as strings
+        return string.Compare(a.ToString(), b.ToString(), StringComparison.Ordinal);
+    }
 
     /// <summary>
     /// SIMD-accelerated row scanning for full table scans.