Fixed SQL Server support for LIMIT and DISTINCT

Resolved bad SQL generated when using LIMIT and DISTINCT in combination
by SQL Server. This method is already hacky as anything... suggestions
welcome!

Author: James Crowley

src/ServiceStack.OrmLite.SqlServer/SqlServerExpressionVisitor.cs

@@ -26,7 +26,9 @@ public override string ToSelectStatement()
 
                 sql = base.ToSelectStatement();
                 if (sql == null || sql.Length < "SELECT".Length) return sql;
-                sql = "SELECT TOP " + take + " " + sql.Substring("SELECT".Length, sql.Length - "SELECT".Length);
+                bool hasDistinctInBaseQuery = sql.StartsWithIgnoreCase("SELECT DISTINCT");
+                string stringToRemoveFromBaseQuery = hasDistinctInBaseQuery ? "SELECT DISTINCT" : "SELECT";
+                sql = stringToRemoveFromBaseQuery + " TOP " + take + " " + sql.Substring(stringToRemoveFromBaseQuery.Length, sql.Length - stringToRemoveFromBaseQuery.Length);
                 return sql;
             }
 

src/ServiceStack.OrmLite.SqlServerTests/Expressions/AuthorUseCase.cs

@@ -224,12 +224,19 @@ public void AuthorUsesCases()
                 Assert.AreEqual("Rodger Contreras".ToUpper(), author.Name);
 
                 // select distinct..
-                ev.Limit().OrderBy(); // clear limit, clear order for postres
+                ev.Limit().OrderBy(); // clear limit, clear orde
                 ev.SelectDistinct(r => r.City);
                 expected = 6;
                 result = db.Select(ev);
                 Assert.AreEqual(expected, result.Count);
 
+                // select distinct with limit
+                ev.Limit(0, 4);
+                ev.SelectDistinct(r => r.City);
+                expected = 4;
+                result = db.Select(ev);
+                Assert.AreEqual(expected, result.Count);
+
                 ev.Select(r => Sql.As(Sql.Max(r.Birthday), "Birthday"));
                 result = db.Select(ev);
                 var expectedResult = authors.Max(r => r.Birthday);