Fix paging in DB2Dialect (#2547)

* Also mark TextHolder as not supported by DB2Dialect

Author: hazzik

src/NHibernate.Test/DialectTest/DB2DialectFixture.cs

@@ -26,7 +26,7 @@ public void GetLimitString()
 
 			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",
+				"select a,b,c 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());
 		}
@@ -58,4 +58,4 @@ public void GetLimitString_NoOffsetSpecified_UsesFetchFirstOnly()
 			Assert.AreEqual(2, limited.GetParameterCount());
 		}
 	}
-}
+}

src/NHibernate.Test/ReadOnly/TextHolder.cs

@@ -10,7 +10,7 @@ public class TextHolder
 		/// </summary>
 		public static bool SupportedForDialect(Dialect.Dialect dialect)
 		{
-			return !(dialect is FirebirdDialect || dialect is Oracle8iDialect || dialect is MsSqlCeDialect || dialect is HanaRowStoreDialect);
+			return !(dialect is FirebirdDialect || dialect is Oracle8iDialect || dialect is MsSqlCeDialect || dialect is HanaRowStoreDialect || dialect is DB2Dialect);
 		}
 
 		private long id;

src/NHibernate/Dialect/DB2Dialect.cs

@@ -232,28 +232,29 @@ public override bool SupportsVariableLimit
 			get { return false; }
 		}
 
-		public override SqlString GetLimitString(SqlString querySqlString, SqlString offset, SqlString limit)
+		public override SqlString GetLimitString(SqlString sql, SqlString offset, SqlString limit)
 		{
 			if (offset == null)
 			{
-				return new SqlString(querySqlString,
-									 " fetch first ",
-									 limit,
-									 " rows only");
+				return new SqlString(sql, " fetch first ", limit, " rows only");
 			}
 
+			ExtractColumnOrAliasNames(sql, out var selectColumns, out _, out _);
+
 			/*
 			 * "select * from (select row_number() over(orderby_clause) as rownum, "
 			 * querySqlString_without select
 			 * " ) as tempresult where rownum between ? and ?"
 			 */
-			string rownumClause = GetRowNumber(querySqlString);
+			string rownumClause = GetRowNumber(sql);
 
 			SqlStringBuilder pagingBuilder = new SqlStringBuilder();
 			pagingBuilder
-				.Add("select * from (select ")
+				.Add("select " )
+				.Add(string.Join(",", selectColumns))
+				.Add(" from (select ")
 				.Add(rownumClause)
-				.Add(querySqlString.Substring(7))
+				.Add(sql.Substring(7))
 				.Add(") as tempresult where rownum ");
 
 			if (limit != null)