diff --git a/expression/builtin_compare.go b/expression/builtin_compare.go
index 800c034b1d886..84088fb13adc2 100644
--- a/expression/builtin_compare.go
+++ b/expression/builtin_compare.go
@@ -470,6 +470,14 @@ func (c *greatestFunctionClass) getFunction(ctx sessionctx.Context, args []Expre
 	}
 	switch tp {
 	case types.ETInt:
+		// adjust unsigned flag
+		greastInitUnsignedFlag := false
+		if isEqualsInitUnsignedFlag(greastInitUnsignedFlag, args) {
+			bf.tp.Flag &= ^mysql.UnsignedFlag
+		} else {
+			bf.tp.Flag |= mysql.UnsignedFlag
+		}
+
 		sig = &builtinGreatestIntSig{bf}
 		sig.setPbCode(tipb.ScalarFuncSig_GreatestInt)
 	case types.ETReal:
@@ -689,6 +697,14 @@ func (c *leastFunctionClass) getFunction(ctx sessionctx.Context, args []Expressi
 	}
 	switch tp {
 	case types.ETInt:
+		// adjust unsigned flag
+		leastInitUnsignedFlag := true
+		if isEqualsInitUnsignedFlag(leastInitUnsignedFlag, args) {
+			bf.tp.Flag |= mysql.UnsignedFlag
+		} else {
+			bf.tp.Flag &= ^mysql.UnsignedFlag
+		}
+
 		sig = &builtinLeastIntSig{bf}
 		sig.setPbCode(tipb.ScalarFuncSig_LeastInt)
 	case types.ETReal:
@@ -2756,3 +2772,15 @@ func CompareJSON(sctx sessionctx.Context, lhsArg, rhsArg Expression, lhsRow, rhs
 	}
 	return int64(json.CompareBinary(arg0, arg1)), false, nil
 }
+
+// isEqualsInitUnsignedFlag can adjust unsigned flag for greatest/least function.
+// For greatest, returns unsigned result if there is at least one argument is unsigned.
+// For least, returns signed result if there is at least one argument is signed.
+func isEqualsInitUnsignedFlag(initUnsigned bool, args []Expression) bool {
+	for _, arg := range args {
+		if initUnsigned != mysql.HasUnsignedFlag(arg.GetType().Flag) {
+			return false
+		}
+	}
+	return true
+}
diff --git a/expression/builtin_compare_test.go b/expression/builtin_compare_test.go
index b8d3db9ae9937..f1aa15ee1a783 100644
--- a/expression/builtin_compare_test.go
+++ b/expression/builtin_compare_test.go
@@ -263,6 +263,8 @@ func (s *testEvaluatorSuite) TestGreatestLeastFunc(c *C) {
 	sc := s.ctx.GetSessionVars().StmtCtx
 	originIgnoreTruncate := sc.IgnoreTruncate
 	sc.IgnoreTruncate = true
+	decG := &types.MyDecimal{}
+	decL := &types.MyDecimal{}
 	defer func() {
 		sc.IgnoreTruncate = originIgnoreTruncate
 	}()
@@ -274,6 +276,14 @@ func (s *testEvaluatorSuite) TestGreatestLeastFunc(c *C) {
 		isNil            bool
 		getErr           bool
 	}{
+		{
+			[]interface{}{int64(-9223372036854775808), uint64(9223372036854775809)},
+			decG.FromUint(9223372036854775809), decL.FromInt(-9223372036854775808), false, false,
+		},
+		{
+			[]interface{}{uint64(9223372036854775808), uint64(9223372036854775809)},
+			uint64(9223372036854775809), uint64(9223372036854775808), false, false,
+		},
 		{
 			[]interface{}{1, 2, 3, 4},
 			int64(4), int64(1), false, false,
diff --git a/expression/integration_test.go b/expression/integration_test.go
index 0032cfa8d20b6..e26e8d850ec17 100644
--- a/expression/integration_test.go
+++ b/expression/integration_test.go
@@ -10318,3 +10318,12 @@ func (s *testIntegrationSuite) TestIssue29244(c *C) {
 	tk.MustExec("set tidb_enable_vectorized_expression = off;")
 	tk.MustQuery("select microsecond(a) from t;").Check(testkit.Rows("123500", "123500"))
 }
+
+func (s *testIntegrationSuite) TestIssue30101(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t1;")
+	tk.MustExec("create table t1(c1 bigint unsigned, c2 bigint unsigned);")
+	tk.MustExec("insert into t1 values(9223372036854775808, 9223372036854775809);")
+	tk.MustQuery("select greatest(c1, c2) from t1;").Sort().Check(testkit.Rows("9223372036854775809"))
+}
diff --git a/expression/typeinfer_test.go b/expression/typeinfer_test.go
index 5365c78f61336..4293241a5ffbd 100644
--- a/expression/typeinfer_test.go
+++ b/expression/typeinfer_test.go
@@ -1034,6 +1034,13 @@ func (s *testInferTypeSuite) createTestCase4CompareFuncs() []typeInferTestCase {
 
 		{"interval(c_int_d, c_int_d, c_int_d)", mysql.TypeLonglong, charset.CharsetBin, mysql.BinaryFlag, mysql.MaxIntWidth, 0},
 		{"interval(c_int_d, c_float_d, c_double_d)", mysql.TypeLonglong, charset.CharsetBin, mysql.BinaryFlag, mysql.MaxIntWidth, 0},
+
+		{"greatest(c_bigint_d, c_ubigint_d, c_int_d)", mysql.TypeNewDecimal, charset.CharsetBin, mysql.BinaryFlag, mysql.MaxIntWidth, 0},
+		{"greatest(c_ubigint_d, c_ubigint_d, c_uint_d)", mysql.TypeLonglong, charset.CharsetBin, mysql.BinaryFlag | mysql.UnsignedFlag, mysql.MaxIntWidth, 0},
+		{"greatest(c_uint_d, c_int_d)", mysql.TypeLonglong, charset.CharsetBin, mysql.BinaryFlag | mysql.UnsignedFlag, 11, 0},
+		{"least(c_bigint_d, c_ubigint_d, c_int_d)", mysql.TypeNewDecimal, charset.CharsetBin, mysql.BinaryFlag, mysql.MaxIntWidth, 0},
+		{"least(c_ubigint_d, c_ubigint_d, c_uint_d)", mysql.TypeLonglong, charset.CharsetBin, mysql.BinaryFlag | mysql.UnsignedFlag, mysql.MaxIntWidth, 0},
+		{"least(c_uint_d, c_int_d)", mysql.TypeLonglong, charset.CharsetBin, mysql.BinaryFlag, 11, 0},
 	}
 }