Fix special NewDecimal type passed from TiDB (#4329)

close #4147

dbms/src/Flash/Coprocessor/DAGUtils.cpp

@@ -990,11 +990,12 @@ String getColumnNameForColumnExpr(const tipb::Expr & expr, const std::vector<Nam
 // So far the known invalid field types are:
 // 1. decimal type with scale == -1
 // 2. decimal type with precision == 0
+// 3. decimal type with precision == -1
 bool exprHasValidFieldType(const tipb::Expr & expr)
 {
     return expr.has_field_type()
         && !(expr.field_type().tp() == TiDB::TP::TypeNewDecimal
-             && (expr.field_type().decimal() == -1 || expr.field_type().flen() == 0));
+             && (expr.field_type().decimal() == -1 || expr.field_type().flen() == 0 || expr.field_type().flen() == -1));
 }
 
 bool isUnsupportedEncodeType(const std::vector<tipb::FieldType> & types, tipb::EncodeType encode_type)

tests/fullstack-test/expr/special_new_decimal_type.test

@@ -0,0 +1,26 @@
+# Copyright 2022 PingCAP, Ltd.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+mysql> drop table if exists test.t
+mysql> create table test.t(a int primary key)
+mysql> alter table test.t set tiflash replica 1
+func> wait_table test t
+mysql> set tidb_enforce_mpp=1; select count(*) from test.t where case when a then isnull(a) else 12.991 end;
++----------+
+| count(*) |
++----------+
+|        0 |
++----------+
+
+mysql> drop table test.t