expression: make group_concat handle character correct (pingcap#2821) (…

…pingcap#3083)

executor/aggregate_test.go

@@ -166,6 +166,11 @@ func (s *testSuite) TestAggregation(c *C) {
 	result = tk.MustQuery("select 1-d as d from t having d + 1 < 0 order by d + 1")
 	result.Check(testkit.Rows("-2", "-2"))
 	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t (keywords varchar(20), type int)")
+	tk.MustExec("insert into t values('测试', 1), ('test', 2)")
+	result = tk.MustQuery("select group_concat(keywords) from t group by type order by type")
+	result.Check(testkit.Rows("测试", "test"))
+	tk.MustExec("drop table if exists t")
 	tk.MustExec("create table t (c int, d int)")
 	tk.MustExec("insert t values (1, -1)")
 	tk.MustExec("insert t values (1, 0)")

expression/aggregation.go

@@ -664,6 +664,14 @@ func (cf *concatFunction) GetType() *types.FieldType {
 	return types.NewFieldType(mysql.TypeVarString)
 }
 
+func (cf *concatFunction) writeValue(ctx *aggEvaluateContext, val types.Datum) {
+	if val.Kind() == types.KindBytes {
+		ctx.Buffer.Write(val.GetBytes())
+	} else {
+		ctx.Buffer.WriteString(fmt.Sprintf("%v", val.GetValue()))
+	}
+}
+
 // Update implements AggregationFunction interface.
 func (cf *concatFunction) Update(row []types.Datum, groupKey []byte, sc *variable.StatementContext) error {
 	ctx := cf.getContext(groupKey)
@@ -694,7 +702,7 @@ func (cf *concatFunction) Update(row []types.Datum, groupKey []byte, sc *variabl
 		ctx.Buffer.WriteString(",")
 	}
 	for _, val := range cf.datumBuf {
-		ctx.Buffer.WriteString(fmt.Sprintf("%v", val.GetValue()))
+		cf.writeValue(ctx, val)
 	}
 	// TODO: if total length is greater than global var group_concat_max_len, truncate it.
 	return nil
@@ -730,7 +738,7 @@ func (cf *concatFunction) StreamUpdate(row []types.Datum, sc *variable.Statement
 		ctx.Buffer.WriteString(",")
 	}
 	for _, val := range cf.datumBuf {
-		ctx.Buffer.WriteString(fmt.Sprintf("%v", val.GetValue()))
+		cf.writeValue(ctx, val)
 	}
 	// TODO: if total length is greater than global var group_concat_max_len, truncate it.
 	return nil