Db2Dialect issues "FETCH FOR N ROWS ONLY" when offset is NOT specified NH-3525

Author: aochsner

src/NHibernate.Test/DialectTest/DB2DialectFixture.cs

@@ -24,11 +24,38 @@ public void GetLimitString()
 						" order by a, x"
 					});
 
-            SqlString limited = dialect.GetLimitString(sql, new SqlString("111"), new SqlString("222"));
+			SqlString limited = dialect.GetLimitString(sql, new SqlString("111"), new SqlString("222"));
 			Assert.AreEqual(
 				"select * from (select rownumber() over(order by a, x) as rownum, a, b, c from d where X = ? and Z = ? order by a, x) as tempresult where rownum between 111+1 and 222",
 				limited.ToString());
 			Assert.AreEqual(2, limited.GetParameterCount());
 		}
+
+		[Test]
+		public void GetLimitString_NoOffsetSpecified_UsesFetchFirstOnly()
+		{
+			// arrange
+			DB2Dialect dialect = new DB2Dialect();
+			SqlString sql = new SqlString(
+				new object[]
+					{
+						"select a, b, c ",
+						"from d",
+						" where X = ",
+						Parameter.Placeholder,
+						" and Z = ",
+						Parameter.Placeholder,
+						" order by a, x"
+					});
+
+			// act
+			SqlString limited = dialect.GetLimitString(sql, null, new SqlString("222"));
+
+			// assert
+			Assert.AreEqual(
+				"select a, b, c from d where X = ? and Z = ? order by a, x fetch first 222 rows only",
+				limited.ToString());
+			Assert.AreEqual(2, limited.GetParameterCount());
+		}
 	}
 }

src/NHibernate/Dialect/DB2Dialect.cs

@@ -208,8 +208,22 @@ public override bool UseMaxForLimit
 			get { return true; }
 		}
 
+		/// <summary></summary>
+		public override bool SupportsVariableLimit
+		{
+			get { return false; }
+		}
+
 		public override SqlString GetLimitString(SqlString querySqlString, SqlString offset, SqlString limit)
 		{
+			if (offset == null)
+			{
+				return new SqlString(querySqlString,
+									 " fetch first ",
+									 limit,
+									 " rows only");
+			}
+
 			/*
 			 * "select * from (select row_number() over(orderby_clause) as rownum, "
 			 * querySqlString_without select
@@ -224,20 +238,14 @@ public override SqlString GetLimitString(SqlString querySqlString, SqlString off
 				.Add(querySqlString.Substring(7))
 				.Add(") as tempresult where rownum ");
 
-			if (offset != null && limit != null)
+			if (limit != null)
 			{
 				pagingBuilder
 					.Add("between ")
 					.Add(offset)
 					.Add("+1 and ")
 					.Add(limit);
 			}
-			else if (limit != null)
-			{
-				pagingBuilder
-					.Add("<= ")
-					.Add(limit);
-			}
 			else
 			{
 				// We just have an offset.