knowledge(performance): grouped query (Count + ColumnFilter = HAVING) for distinct values and duplicates (#215)

Adds use-grouped-query-for-distinct-values-and-duplicates with good/bad
samples, a worklist cue in al-performance-review, and registration in the
performance review-fixtures override.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

microsoft/knowledge/performance/use-grouped-query-for-distinct-values-and-duplicates.good.al

@@ -0,0 +1,47 @@
+// One row per customer name that occurs more than once.
+// Name is a plain column, so it is the grouping key; the ColumnFilter on the
+// Count column is applied after grouping (HAVING COUNT(*) > 1).
+query 50570 "Duplicate Customer Names"
+{
+    QueryType = Normal;
+
+    elements
+    {
+        dataitem(Customer; Customer)
+        {
+            column(Name; Name)
+            {
+                ColumnFilter = Name = filter(<> '');
+            }
+            column(NameCount)
+            {
+                Method = Count;
+                ColumnFilter = NameCount = filter(> 1);
+            }
+        }
+    }
+}
+
+codeunit 50571 "Customer Name Review"
+{
+    procedure HasDuplicateCustomerNames(): Boolean
+    var
+        DuplicateCustomerNames: Query "Duplicate Customer Names";
+        Found: Boolean;
+    begin
+        DuplicateCustomerNames.Open();
+        Found := DuplicateCustomerNames.Read();
+        DuplicateCustomerNames.Close();
+        exit(Found);
+    end;
+
+    procedure GetDuplicateCustomerNames(var DuplicateNames: List of [Text])
+    var
+        DuplicateCustomerNames: Query "Duplicate Customer Names";
+    begin
+        DuplicateCustomerNames.Open();
+        while DuplicateCustomerNames.Read() do
+            DuplicateNames.Add(DuplicateCustomerNames.Name);
+        DuplicateCustomerNames.Close();
+    end;
+}