From c17edb149375e320e62725453a26bcd5236a0f90 Mon Sep 17 00:00:00 2001
From: HuaiyuXu <391585975@qq.com>
Date: Mon, 8 Jan 2018 17:26:27 +0800
Subject: [PATCH] expression: refine the type infer of group_concat (#5582)

---
 expression/aggregation/concat.go | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/expression/aggregation/concat.go b/expression/aggregation/concat.go
index fc81fad23edde..3b83f6f1b702c 100644
--- a/expression/aggregation/concat.go
+++ b/expression/aggregation/concat.go
@@ -20,6 +20,7 @@ import (
 	"github.com/juju/errors"
 	"github.com/pingcap/tidb/mysql"
 	"github.com/pingcap/tidb/sessionctx/variable"
+	"github.com/pingcap/tidb/util/charset"
 	"github.com/pingcap/tidb/util/types"
 )
 
@@ -40,7 +41,11 @@ func (cf *concatFunction) Clone() Aggregation {
 
 // GetType implements Aggregation interface.
 func (cf *concatFunction) GetType() *types.FieldType {
-	return types.NewFieldType(mysql.TypeVarString)
+	retType := types.NewFieldType(mysql.TypeVarString)
+	retType.Charset = charset.CharsetUTF8
+	retType.Collate = charset.CollationUTF8
+	retType.Flen, retType.Decimal = mysql.MaxBlobWidth, 0
+	return retType
 }
 
 func (cf *concatFunction) writeValue(ctx *AggEvaluateContext, val types.Datum) {