expression: return upper bound for enum (pingcap#41021)

close pingcap#40855

Author: YangKeao

expression/builtin_compare_test.go

@@ -406,3 +406,17 @@ func TestGreatestLeastFunc(t *testing.T) {
 	_, err = funcs[ast.Least].getFunction(ctx, []Expression{NewZero(), NewOne()})
 	require.NoError(t, err)
 }
+
+func TestRefineArgsWithCastEnum(t *testing.T) {
+	ctx := createContext(t)
+	zeroUintConst := primitiveValsToConstants(ctx, []interface{}{uint64(0)})[0]
+	enumType := types.NewFieldTypeBuilder().SetType(mysql.TypeEnum).SetElems([]string{"1", "2", "3"}).AddFlag(mysql.EnumSetAsIntFlag).Build()
+	enumCol := &Column{RetType: &enumType}
+
+	f := funcs[ast.EQ].(*compareFunctionClass)
+	require.NotNil(t, f)
+
+	args := f.refineArgsByUnsignedFlag(ctx, []Expression{zeroUintConst, enumCol})
+	require.Equal(t, zeroUintConst, args[0])
+	require.Equal(t, enumCol, args[1])
+}

types/convert.go

@@ -52,7 +52,9 @@ func IntergerUnsignedUpperBound(intType byte) uint64 {
 	case mysql.TypeBit:
 		return math.MaxUint64
 	case mysql.TypeEnum:
-		return math.MaxUint64
+		// enum can have at most 65535 distinct elements
+		// it would be better to use len(FieldType.GetElems()), but we only have a byte type here
+		return 65535
 	case mysql.TypeSet:
 		return math.MaxUint64
 	default:
@@ -73,8 +75,12 @@ func IntergerSignedUpperBound(intType byte) int64 {
 		return math.MaxInt32
 	case mysql.TypeLonglong:
 		return math.MaxInt64
+	case mysql.TypeEnum:
+		// enum can have at most 65535 distinct elements
+		// it would be better to use len(FieldType.GetElems()), but we only have a byte type here
+		return 65535
 	default:
-		panic("Input byte is not a mysql type")
+		panic("Input byte is not a mysql int type")
 	}
 }
 
@@ -91,6 +97,8 @@ func IntergerSignedLowerBound(intType byte) int64 {
 		return math.MinInt32
 	case mysql.TypeLonglong:
 		return math.MinInt64
+	case mysql.TypeEnum:
+		return 0
 	default:
 		panic("Input byte is not a mysql type")
 	}