expression: forbid aggregate function with json type pushdown to tiflash wrongly

expression/aggregation/aggregation.go

@@ -222,8 +222,11 @@ func CheckAggPushFlash(aggFunc *AggFuncDesc) bool {
 		}
 	}
 	switch aggFunc.Name {
-	case ast.AggFuncSum, ast.AggFuncCount, ast.AggFuncMin, ast.AggFuncMax, ast.AggFuncAvg, ast.AggFuncFirstRow, ast.AggFuncApproxCountDistinct, ast.AggFuncGroupConcat:
+	case ast.AggFuncCount, ast.AggFuncMin, ast.AggFuncMax, ast.AggFuncFirstRow, ast.AggFuncApproxCountDistinct:
 		return true
+	case ast.AggFuncSum, ast.AggFuncAvg, ast.AggFuncGroupConcat:
+		// Now tiflash doesn't support CastJsonAsReal and CastJsonAsString.
+		return aggFunc.Args[0].GetType().GetType() != mysql.TypeJSON
 	}
 	return false
 }

planner/core/integration_test.go

@@ -7117,3 +7117,53 @@ func TestGetFormatPushDownToTiFlash(t *testing.T) {
 		"  └─Projection 10000.00 mpp[tiflash]  get_format(DATE, test.t.location)->Column#3",
 		"    └─TableFullScan 10000.00 mpp[tiflash] table:t keep order:false, stats:pseudo"))
 }
+
+func TestAggWithJsonPushDownToTiFlash(t *testing.T) {
+	store, clean := testkit.CreateMockStore(t)
+	defer clean()
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t(a json);")
+	tk.MustExec("insert into t values(null);")
+	tk.MustExec("set @@tidb_allow_mpp=1; set @@tidb_enforce_mpp=1;")
+	tk.MustExec("set @@tidb_isolation_read_engines = 'tiflash'")
+
+	// Create virtual tiflash replica info.
+	dom := domain.GetDomain(tk.Session())
+	is := dom.InfoSchema()
+	db, exists := is.SchemaByName(model.NewCIStr("test"))
+	require.True(t, exists)
+	for _, tblInfo := range db.Tables {
+		if tblInfo.Name.L == "t" {
+			tblInfo.TiFlashReplica = &model.TiFlashReplicaInfo{
+				Count:     1,
+				Available: true,
+			}
+		}
+	}
+
+	rows := [][]interface{}{
+		{"HashAgg_6", "root", "funcs:avg(Column#4)->Column#3"},
+		{"└─Projection_19", "root", "cast(test.t.a, double BINARY)->Column#4"},
+		{"  └─TableReader_12", "root", "data:TableFullScan_11"},
+		{"    └─TableFullScan_11", "cop[tiflash]", "keep order:false, stats:pseudo"},
+	}
+	tk.MustQuery("explain select avg(a) from t;").CheckAt([]int{0, 2, 4}, rows)
+
+	rows = [][]interface{}{
+		{"HashAgg_6", "root", "funcs:sum(Column#4)->Column#3"},
+		{"└─Projection_19", "root", "cast(test.t.a, double BINARY)->Column#4"},
+		{"  └─TableReader_12", "root", "data:TableFullScan_11"},
+		{"    └─TableFullScan_11", "cop[tiflash]", "keep order:false, stats:pseudo"},
+	}
+	tk.MustQuery("explain select sum(a) from t;").CheckAt([]int{0, 2, 4}, rows)
+
+	rows = [][]interface{}{
+		{"HashAgg_6", "root", "funcs:group_concat(Column#4 separator \",\")->Column#3"},
+		{"└─Projection_13", "root", "cast(test.t.a, var_string(4294967295))->Column#4"},
+		{"  └─TableReader_10", "root", "data:TableFullScan_9"},
+		{"    └─TableFullScan_9", "cop[tiflash]", "keep order:false, stats:pseudo"},
+	}
+	tk.MustQuery("explain select /*+ hash_agg() */  group_concat(a) from t;").CheckAt([]int{0, 2, 4}, rows)
+}