diff --git a/executor/executor_test.go b/executor/executor_test.go
index d12591ec9e7cf..d3027057f3ff5 100644
--- a/executor/executor_test.go
+++ b/executor/executor_test.go
@@ -1399,6 +1399,12 @@ func (s *testSuiteP2) TestUnion(c *C) {
 	tk.MustExec("create table t(a int, b decimal(6, 3))")
 	tk.MustExec("insert into t values(1, 1.000)")
 	tk.MustQuery("select count(distinct a), sum(distinct a), avg(distinct a) from (select a from t union all select b from t) tmp;").Check(testkit.Rows("1 1.000 1.0000000"))
+
+	// #issue 23832
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t(a bit(20), b float, c double, d int)")
+	tk.MustExec("insert into t values(10, 10, 10, 10), (1, -1, 2, -2), (2, -2, 1, 1), (2, 1.1, 2.1, 10.1)")
+	tk.MustQuery("select a from t union select 10 order by a").Check(testkit.Rows("1", "2", "10"))
 }
 
 func (s *testSuite2) TestUnionLimit(c *C) {
diff --git a/types/field_type.go b/types/field_type.go
index 0cc65b60f2e53..5804e38c3069e 100644
--- a/types/field_type.go
+++ b/types/field_type.go
@@ -330,7 +330,7 @@ func DefaultCharsetForType(tp byte) (string, string) {
 // This is used in hybrid field type expression.
 // For example "select case c when 1 then 2 when 2 then 'tidb' from t;"
 // The result field type of the case expression is the merged type of the two when clause.
-// See https://github.com/mysql/mysql-server/blob/5.7/sql/field.cc#L1042
+// See https://github.com/mysql/mysql-server/blob/8.0/sql/field.cc#L1042
 func MergeFieldType(a byte, b byte) byte {
 	ia := getFieldTypeIndex(a)
 	ib := getFieldTypeIndex(b)
@@ -358,6 +358,7 @@ const (
 	fieldTypeNum      = fieldTypeTearFrom + (255 - fieldTypeTearTo)
 )
 
+// https://github.com/mysql/mysql-server/blob/8.0/sql/field.cc#L248
 var fieldTypeMergeRules = [fieldTypeNum][fieldTypeNum]byte{
 	/* mysql.TypeDecimal -> */
 	{
@@ -410,9 +411,9 @@ var fieldTypeMergeRules = [fieldTypeNum][fieldTypeNum]byte{
 		mysql.TypeVarchar, mysql.TypeTiny,
 		//mysql.TypeNewDate      mysql.TypeVarchar
 		mysql.TypeVarchar, mysql.TypeVarchar,
-		//mysql.TypeBit          <16>-<244>
-		mysql.TypeVarchar,
-		//mysql.TypeJSON
+		// mysql.TypeBit          <16>-<244>
+		mysql.TypeLonglong,
+		// mysql.TypeJSON
 		mysql.TypeVarchar,
 		//mysql.TypeNewDecimal   mysql.TypeEnum
 		mysql.TypeNewDecimal, mysql.TypeVarchar,
@@ -443,9 +444,9 @@ var fieldTypeMergeRules = [fieldTypeNum][fieldTypeNum]byte{
 		mysql.TypeVarchar, mysql.TypeShort,
 		//mysql.TypeNewDate      mysql.TypeVarchar
 		mysql.TypeVarchar, mysql.TypeVarchar,
-		//mysql.TypeBit          <16>-<244>
-		mysql.TypeVarchar,
-		//mysql.TypeJSON
+		// mysql.TypeBit          <16>-<244>
+		mysql.TypeLonglong,
+		// mysql.TypeJSON
 		mysql.TypeVarchar,
 		//mysql.TypeNewDecimal   mysql.TypeEnum
 		mysql.TypeNewDecimal, mysql.TypeVarchar,
@@ -476,9 +477,9 @@ var fieldTypeMergeRules = [fieldTypeNum][fieldTypeNum]byte{
 		mysql.TypeVarchar, mysql.TypeLong,
 		//mysql.TypeNewDate      mysql.TypeVarchar
 		mysql.TypeVarchar, mysql.TypeVarchar,
-		//mysql.TypeBit          <16>-<244>
-		mysql.TypeVarchar,
-		//mysql.TypeJSON
+		// mysql.TypeBit          <16>-<244>
+		mysql.TypeLonglong,
+		// mysql.TypeJSON
 		mysql.TypeVarchar,
 		//mysql.TypeNewDecimal   mysql.TypeEnum
 		mysql.TypeNewDecimal, mysql.TypeVarchar,
@@ -509,9 +510,9 @@ var fieldTypeMergeRules = [fieldTypeNum][fieldTypeNum]byte{
 		mysql.TypeVarchar, mysql.TypeFloat,
 		//mysql.TypeNewDate      mysql.TypeVarchar
 		mysql.TypeVarchar, mysql.TypeVarchar,
-		//mysql.TypeBit          <16>-<244>
-		mysql.TypeVarchar,
-		//mysql.TypeJSON
+		// mysql.TypeBit          <16>-<244>
+		mysql.TypeDouble,
+		// mysql.TypeJSON
 		mysql.TypeVarchar,
 		//mysql.TypeNewDecimal   mysql.TypeEnum
 		mysql.TypeDouble, mysql.TypeVarchar,
@@ -542,9 +543,9 @@ var fieldTypeMergeRules = [fieldTypeNum][fieldTypeNum]byte{
 		mysql.TypeVarchar, mysql.TypeDouble,
 		//mysql.TypeNewDate      mysql.TypeVarchar
 		mysql.TypeVarchar, mysql.TypeVarchar,
-		//mysql.TypeBit          <16>-<244>
-		mysql.TypeVarchar,
-		//mysql.TypeJSON
+		// mysql.TypeBit          <16>-<244>
+		mysql.TypeDouble,
+		// mysql.TypeJSON
 		mysql.TypeVarchar,
 		//mysql.TypeNewDecimal   mysql.TypeEnum
 		mysql.TypeDouble, mysql.TypeVarchar,
@@ -641,9 +642,9 @@ var fieldTypeMergeRules = [fieldTypeNum][fieldTypeNum]byte{
 		mysql.TypeVarchar, mysql.TypeLonglong,
 		//mysql.TypeNewDate      mysql.TypeVarchar
 		mysql.TypeNewDate, mysql.TypeVarchar,
-		//mysql.TypeBit          <16>-<244>
-		mysql.TypeVarchar,
-		//mysql.TypeJSON
+		// mysql.TypeBit          <16>-<244>
+		mysql.TypeLonglong,
+		// mysql.TypeJSON
 		mysql.TypeVarchar,
 		//mysql.TypeNewDecimal   mysql.TypeEnum
 		mysql.TypeNewDecimal, mysql.TypeVarchar,
@@ -674,9 +675,9 @@ var fieldTypeMergeRules = [fieldTypeNum][fieldTypeNum]byte{
 		mysql.TypeVarchar, mysql.TypeInt24,
 		//mysql.TypeNewDate      mysql.TypeVarchar
 		mysql.TypeNewDate, mysql.TypeVarchar,
-		//mysql.TypeBit          <16>-<244>
-		mysql.TypeVarchar,
-		//mysql.TypeJSON
+		// mysql.TypeBit          <16>-<244>
+		mysql.TypeLonglong,
+		// mysql.TypeJSON
 		mysql.TypeVarchar,
 		//mysql.TypeNewDecimal    mysql.TypeEnum
 		mysql.TypeNewDecimal, mysql.TypeVarchar,
@@ -806,9 +807,9 @@ var fieldTypeMergeRules = [fieldTypeNum][fieldTypeNum]byte{
 		mysql.TypeVarchar, mysql.TypeYear,
 		//mysql.TypeNewDate      mysql.TypeVarchar
 		mysql.TypeVarchar, mysql.TypeVarchar,
-		//mysql.TypeBit          <16>-<244>
-		mysql.TypeVarchar,
-		//mysql.TypeJSON
+		// mysql.TypeBit          <16>-<244>
+		mysql.TypeLonglong,
+		// mysql.TypeJSON
 		mysql.TypeVarchar,
 		//mysql.TypeNewDecimal   mysql.TypeEnum
 		mysql.TypeNewDecimal, mysql.TypeVarchar,
@@ -889,29 +890,29 @@ var fieldTypeMergeRules = [fieldTypeNum][fieldTypeNum]byte{
 	},
 	/* mysql.TypeBit -> */
 	{
-		//mysql.TypeDecimal      mysql.TypeTiny
-		mysql.TypeVarchar, mysql.TypeVarchar,
-		//mysql.TypeShort        mysql.TypeLong
-		mysql.TypeVarchar, mysql.TypeVarchar,
-		//mysql.TypeFloat        mysql.TypeDouble
-		mysql.TypeVarchar, mysql.TypeVarchar,
-		//mysql.TypeNull         mysql.TypeTimestamp
+		// mysql.TypeUnspecified  mysql.TypeTiny
+		mysql.TypeVarchar, mysql.TypeLonglong,
+		// mysql.TypeShort        mysql.TypeLong
+		mysql.TypeLonglong, mysql.TypeLonglong,
+		// mysql.TypeFloat        mysql.TypeDouble
+		mysql.TypeDouble, mysql.TypeDouble,
+		// mysql.TypeNull         mysql.TypeTimestamp
 		mysql.TypeBit, mysql.TypeVarchar,
-		//mysql.TypeLonglong     mysql.TypeInt24
-		mysql.TypeVarchar, mysql.TypeVarchar,
-		//mysql.TypeDate         mysql.TypeTime
-		mysql.TypeVarchar, mysql.TypeVarchar,
-		//mysql.TypeDatetime     mysql.TypeYear
+		// mysql.TypeLonglong     mysql.TypeInt24
+		mysql.TypeLonglong, mysql.TypeLonglong,
+		// mysql.TypeDate         mysql.TypeTime
 		mysql.TypeVarchar, mysql.TypeVarchar,
-		//mysql.TypeNewDate      mysql.TypeVarchar
+		// mysql.TypeDatetime     mysql.TypeYear
+		mysql.TypeVarchar, mysql.TypeLonglong,
+		// mysql.TypeNewDate      mysql.TypeVarchar
 		mysql.TypeVarchar, mysql.TypeVarchar,
 		//mysql.TypeBit          <16>-<244>
 		mysql.TypeBit,
 		//mysql.TypeJSON
 		mysql.TypeVarchar,
-		//mysql.TypeNewDecimal   mysql.TypeEnum
-		mysql.TypeVarchar, mysql.TypeVarchar,
-		//mysql.TypeSet          mysql.TypeTinyBlob
+		// mysql.TypeNewDecimal   mysql.TypeEnum
+		mysql.TypeNewDecimal, mysql.TypeVarchar,
+		// mysql.TypeSet          mysql.TypeTinyBlob
 		mysql.TypeVarchar, mysql.TypeTinyBlob,
 		//mysql.TypeMediumBlob  mysql.TypeLongBlob
 		mysql.TypeMediumBlob, mysql.TypeLongBlob,
@@ -971,9 +972,9 @@ var fieldTypeMergeRules = [fieldTypeNum][fieldTypeNum]byte{
 		mysql.TypeVarchar, mysql.TypeNewDecimal,
 		//mysql.TypeNewDate      mysql.TypeVarchar
 		mysql.TypeVarchar, mysql.TypeVarchar,
-		//mysql.TypeBit          <16>-<244>
-		mysql.TypeVarchar,
-		//mysql.TypeJSON
+		// mysql.TypeBit          <16>-<244>
+		mysql.TypeNewDecimal,
+		// mysql.TypeJSON
 		mysql.TypeVarchar,
 		//mysql.TypeNewDecimal   mysql.TypeEnum
 		mysql.TypeNewDecimal, mysql.TypeVarchar,
diff --git a/types/field_type_test.go b/types/field_type_test.go
index 4d2583ec97d97..821ef86b36899 100644
--- a/types/field_type_test.go
+++ b/types/field_type_test.go
@@ -270,9 +270,11 @@ func (s *testFieldTypeSuite) TestAggFieldType(c *C) {
 			c.Assert(aggTp.Tp, Equals, mysql.TypeDouble)
 		case mysql.TypeTimestamp, mysql.TypeDate, mysql.TypeDuration,
 			mysql.TypeDatetime, mysql.TypeNewDate, mysql.TypeVarchar,
-			mysql.TypeBit, mysql.TypeJSON, mysql.TypeEnum, mysql.TypeSet,
+			mysql.TypeJSON, mysql.TypeEnum, mysql.TypeSet,
 			mysql.TypeVarString, mysql.TypeGeometry:
 			c.Assert(aggTp.Tp, Equals, mysql.TypeVarchar)
+		case mysql.TypeBit:
+			c.Assert(aggTp.Tp, Equals, mysql.TypeLonglong)
 		case mysql.TypeString:
 			c.Assert(aggTp.Tp, Equals, mysql.TypeString)
 		case mysql.TypeDecimal, mysql.TypeNewDecimal: