diff --git a/executor/join_test.go b/executor/join_test.go
index a930ae1af9..c62f1ffaeb 100644
--- a/executor/join_test.go
+++ b/executor/join_test.go
@@ -300,6 +300,17 @@ func (s *testSuite) TestJoinCast(c *C) {
 	tk.MustExec("insert into t1 values(0), (9)")
 	result = tk.MustQuery("select /*+ TIDB_INLJ(t) */ * from t left join t1 on t1.c1 = t.c1")
 	result.Sort().Check(testkit.Rows("0.0 0.00", "2.0 <nil>"))
+
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("drop table if exists t1")
+	tk.MustExec("create table t(c1 char(10))")
+	tk.MustExec("create table t1(c1 char(10))")
+	tk.MustExec("create table t2(c1 char(10))")
+	tk.MustExec("insert into t values('abd')")
+	tk.MustExec("insert into t1 values('abc')")
+	tk.MustExec("insert into t2 values('abc')")
+	result = tk.MustQuery("select * from (select * from t union all select * from t1) t1 join t2 on t1.c1 = t2.c1")
+	result.Sort().Check(testkit.Rows("abc abc"))
 }
 
 func (s *testSuite) TestUsing(c *C) {
diff --git a/expression/builtin_string.go b/expression/builtin_string.go
index 8005aaba98..f8d31e23fe 100644
--- a/expression/builtin_string.go
+++ b/expression/builtin_string.go
@@ -155,9 +155,9 @@ func reverseRunes(origin []rune) []rune {
 	return origin
 }
 
-// setBinFlagOrBinStr sets resTp to binary string if argTp is a binary string,
+// SetBinFlagOrBinStr sets resTp to binary string if argTp is a binary string,
 // if not, sets the binary flag of resTp to true if argTp has binary flag.
-func setBinFlagOrBinStr(argTp *types.FieldType, resTp *types.FieldType) {
+func SetBinFlagOrBinStr(argTp *types.FieldType, resTp *types.FieldType) {
 	if types.IsBinaryStr(argTp) {
 		types.SetBinChsClnFlag(resTp)
 	} else if mysql.HasBinaryFlag(argTp.Flag) {
@@ -248,7 +248,7 @@ func (c *concatFunctionClass) getFunction(args []Expression, ctx context.Context
 	}
 	for i := range args {
 		argType := args[i].GetType()
-		setBinFlagOrBinStr(argType, bf.tp)
+		SetBinFlagOrBinStr(argType, bf.tp)
 
 		if argType.Flen < 0 {
 			bf.tp.Flen = mysql.MaxBlobWidth
@@ -300,7 +300,7 @@ func (c *concatWSFunctionClass) getFunction(args []Expression, ctx context.Conte
 
 	for i := range args {
 		argType := args[i].GetType()
-		setBinFlagOrBinStr(argType, bf.tp)
+		SetBinFlagOrBinStr(argType, bf.tp)
 
 		// skip seperator param
 		if i != 0 {
@@ -375,7 +375,7 @@ func (c *leftFunctionClass) getFunction(args []Expression, ctx context.Context)
 	}
 	argType := args[0].GetType()
 	bf.tp.Flen = argType.Flen
-	setBinFlagOrBinStr(argType, bf.tp)
+	SetBinFlagOrBinStr(argType, bf.tp)
 	if types.IsBinaryStr(argType) {
 		sig := &builtinLeftBinarySig{baseStringBuiltinFunc{bf}}
 		return sig.setSelf(sig), nil
@@ -448,7 +448,7 @@ func (c *rightFunctionClass) getFunction(args []Expression, ctx context.Context)
 	}
 	argType := args[0].GetType()
 	bf.tp.Flen = argType.Flen
-	setBinFlagOrBinStr(argType, bf.tp)
+	SetBinFlagOrBinStr(argType, bf.tp)
 	if types.IsBinaryStr(argType) {
 		sig := &builtinRightBinarySig{baseStringBuiltinFunc{bf}}
 		return sig.setSelf(sig), nil
@@ -521,7 +521,7 @@ func (c *repeatFunctionClass) getFunction(args []Expression, ctx context.Context
 		return nil, errors.Trace(err)
 	}
 	bf.tp.Flen = mysql.MaxBlobWidth
-	setBinFlagOrBinStr(args[0].GetType(), bf.tp)
+	SetBinFlagOrBinStr(args[0].GetType(), bf.tp)
 	sig := &builtinRepeatSig{baseStringBuiltinFunc{bf}}
 	return sig.setSelf(sig), nil
 }
@@ -570,7 +570,7 @@ func (c *lowerFunctionClass) getFunction(args []Expression, ctx context.Context)
 	}
 	argTp := args[0].GetType()
 	bf.tp.Flen = argTp.Flen
-	setBinFlagOrBinStr(argTp, bf.tp)
+	SetBinFlagOrBinStr(argTp, bf.tp)
 	sig := &builtinLowerSig{baseStringBuiltinFunc{bf}}
 	return sig.setSelf(sig), nil
 }
@@ -699,7 +699,7 @@ func (c *upperFunctionClass) getFunction(args []Expression, ctx context.Context)
 	}
 	argTp := args[0].GetType()
 	bf.tp.Flen = argTp.Flen
-	setBinFlagOrBinStr(argTp, bf.tp)
+	SetBinFlagOrBinStr(argTp, bf.tp)
 	sig := &builtinUpperSig{baseStringBuiltinFunc{bf}}
 	return sig.setSelf(sig), nil
 }
@@ -781,7 +781,7 @@ func (c *replaceFunctionClass) getFunction(args []Expression, ctx context.Contex
 	}
 	bf.tp.Flen = c.fixLength(args)
 	for _, a := range args {
-		setBinFlagOrBinStr(a.GetType(), bf.tp)
+		SetBinFlagOrBinStr(a.GetType(), bf.tp)
 	}
 	sig := &builtinReplaceSig{baseStringBuiltinFunc{bf}}
 	return sig.setSelf(sig), nil
@@ -898,7 +898,7 @@ func (c *substringFunctionClass) getFunction(args []Expression, ctx context.Cont
 
 	argType := args[0].GetType()
 	bf.tp.Flen = argType.Flen
-	setBinFlagOrBinStr(argType, bf.tp)
+	SetBinFlagOrBinStr(argType, bf.tp)
 
 	var sig builtinFunc
 	switch {
@@ -1065,7 +1065,7 @@ func (c *substringIndexFunctionClass) getFunction(args []Expression, ctx context
 	}
 	argType := args[0].GetType()
 	bf.tp.Flen = argType.Flen
-	setBinFlagOrBinStr(argType, bf.tp)
+	SetBinFlagOrBinStr(argType, bf.tp)
 	sig := &builtinSubstringIndexSig{baseStringBuiltinFunc{bf}}
 	return sig.setSelf(sig), nil
 }
@@ -1421,7 +1421,7 @@ func (c *trimFunctionClass) getFunction(args []Expression, ctx context.Context)
 		}
 		argType := args[0].GetType()
 		bf.tp.Flen = argType.Flen
-		setBinFlagOrBinStr(argType, bf.tp)
+		SetBinFlagOrBinStr(argType, bf.tp)
 		sig := &builtinTrim1ArgSig{baseStringBuiltinFunc{bf}}
 		return sig.setSelf(sig), nil
 
@@ -1431,7 +1431,7 @@ func (c *trimFunctionClass) getFunction(args []Expression, ctx context.Context)
 			return nil, errors.Trace(err)
 		}
 		argType := args[0].GetType()
-		setBinFlagOrBinStr(argType, bf.tp)
+		SetBinFlagOrBinStr(argType, bf.tp)
 		sig := &builtinTrim2ArgsSig{baseStringBuiltinFunc{bf}}
 		return sig.setSelf(sig), nil
 
@@ -1442,7 +1442,7 @@ func (c *trimFunctionClass) getFunction(args []Expression, ctx context.Context)
 		}
 		argType := args[0].GetType()
 		bf.tp.Flen = argType.Flen
-		setBinFlagOrBinStr(argType, bf.tp)
+		SetBinFlagOrBinStr(argType, bf.tp)
 		sig := &builtinTrim3ArgsSig{baseStringBuiltinFunc{bf}}
 		return sig.setSelf(sig), nil
 
@@ -1552,7 +1552,7 @@ func (c *lTrimFunctionClass) getFunction(args []Expression, ctx context.Context)
 	}
 	argType := args[0].GetType()
 	bf.tp.Flen = argType.Flen
-	setBinFlagOrBinStr(argType, bf.tp)
+	SetBinFlagOrBinStr(argType, bf.tp)
 	sig := &builtinLTrimSig{baseStringBuiltinFunc{bf}}
 	return sig.setSelf(sig), nil
 }
@@ -1585,7 +1585,7 @@ func (c *rTrimFunctionClass) getFunction(args []Expression, ctx context.Context)
 	}
 	argType := args[0].GetType()
 	bf.tp.Flen = argType.Flen
-	setBinFlagOrBinStr(argType, bf.tp)
+	SetBinFlagOrBinStr(argType, bf.tp)
 	sig := &builtinRTrimSig{baseStringBuiltinFunc{bf}}
 	return sig.setSelf(sig), nil
 }
@@ -1651,8 +1651,8 @@ func (c *lpadFunctionClass) getFunction(args []Expression, ctx context.Context)
 		return nil, errors.Trace(err)
 	}
 	bf.tp.Flen = getFlen4LpadAndRpad(bf.ctx.GetSessionVars().StmtCtx, args[1])
-	setBinFlagOrBinStr(args[0].GetType(), bf.tp)
-	setBinFlagOrBinStr(args[2].GetType(), bf.tp)
+	SetBinFlagOrBinStr(args[0].GetType(), bf.tp)
+	SetBinFlagOrBinStr(args[2].GetType(), bf.tp)
 	if types.IsBinaryStr(args[0].GetType()) || types.IsBinaryStr(args[2].GetType()) {
 		sig := &builtinLpadBinarySig{baseStringBuiltinFunc{bf}}
 		return sig.setSelf(sig), nil
@@ -1756,8 +1756,8 @@ func (c *rpadFunctionClass) getFunction(args []Expression, ctx context.Context)
 	if err != nil {
 		return nil, errors.Trace(err)
 	}
-	setBinFlagOrBinStr(args[0].GetType(), bf.tp)
-	setBinFlagOrBinStr(args[2].GetType(), bf.tp)
+	SetBinFlagOrBinStr(args[0].GetType(), bf.tp)
+	SetBinFlagOrBinStr(args[2].GetType(), bf.tp)
 	if types.IsBinaryStr(args[0].GetType()) || types.IsBinaryStr(args[2].GetType()) {
 		sig := &builtinRpadBinarySig{baseStringBuiltinFunc{bf}}
 		return sig.setSelf(sig), nil
diff --git a/plan/logical_plan_builder.go b/plan/logical_plan_builder.go
index bbb68985bc..9a9df3962d 100644
--- a/plan/logical_plan_builder.go
+++ b/plan/logical_plan_builder.go
@@ -532,6 +532,9 @@ func joinFieldType(a, b *types.FieldType) *types.FieldType {
 	resultTp.Decimal = mathutil.Max(a.Decimal, b.Decimal)
 	// `Flen - Decimal` is the fraction before '.'
 	resultTp.Flen = mathutil.Max(a.Flen-a.Decimal, b.Flen-b.Decimal) + resultTp.Decimal
+	resultTp.Charset = a.Charset
+	resultTp.Collate = a.Collate
+	expression.SetBinFlagOrBinStr(b, resultTp)
 	return resultTp
 }