expression: fix WEEK NULL mode handling (#68440)

close #59444

Author: hawkingrei

pkg/expression/builtin_time.go

@@ -1463,9 +1463,13 @@ func (b *builtinWeekWithModeSig) evalInt(ctx EvalContext, row chunk.Row) (int64,
 	}
 
 	mode, isNull, err := b.args[1].EvalInt(ctx, row)
-	if isNull || err != nil {
+	if err != nil {
 		return 0, isNull, err
 	}
+	if isNull {
+		// MySQL treats a NULL week mode as mode 0 for WEEK(date, mode).
+		mode = 0
+	}
 
 	week := date.Week(int(mode))
 	return int64(week), false, nil

pkg/expression/builtin_time_test.go

@@ -2054,6 +2054,16 @@ func TestWeek(t *testing.T) {
 		require.NoError(t, err)
 		require.Equal(t, test.expect, result.GetInt64())
 	}
+
+	f, err := fc.getFunction(ctx, datumsToConstants([]types.Datum{
+		types.NewStringDatum("2023-01-01"),
+		types.NewDatum(nil),
+	}))
+	require.NoError(t, err)
+	result, err := evalBuiltinFunc(f, ctx, chunk.Row{})
+	require.NoError(t, err)
+	require.False(t, result.IsNull())
+	require.Equal(t, int64(1), result.GetInt64())
 }
 
 func TestWeekWithoutModeSig(t *testing.T) {

pkg/expression/builtin_time_vec.go

@@ -1027,11 +1027,11 @@ func (b *builtinWeekWithModeSig) vecEvalInt(ctx EvalContext, input *chunk.Chunk,
 			result.SetNull(i, true)
 			continue
 		}
+		mode := int(ms[i])
 		if buf2.IsNull(i) {
-			result.SetNull(i, true)
-			continue
+			// MySQL treats a NULL week mode as mode 0 for WEEK(date, mode).
+			mode = 0
 		}
-		mode := int(ms[i])
 		week := date.Week(mode)
 		i64s[i] = int64(week)
 	}

pkg/expression/builtin_time_vec_test.go

@@ -392,6 +392,8 @@ var vecBuiltinTimeCases = map[string][]vecExprBenchCase{
 	ast.Week: {
 		{retEvalType: types.ETInt, childrenTypes: []types.EvalType{types.ETDatetime}},
 		{retEvalType: types.ETInt, childrenTypes: []types.EvalType{types.ETDatetime, types.ETInt}},
+		{retEvalType: types.ETInt, childrenTypes: []types.EvalType{types.ETDatetime, types.ETInt},
+			constants: []*Constant{nil, {Value: types.NewDatum(nil), RetType: types.NewFieldType(mysql.TypeLonglong)}}},
 	},
 	ast.Month: {
 		{retEvalType: types.ETInt, childrenTypes: []types.EvalType{types.ETDatetime}},

pkg/expression/integration_test/integration_test.go

@@ -2934,6 +2934,9 @@ func TestTimeBuiltin(t *testing.T) {
 	result.Check(testkit.Rows("7 7 8 7 8 8"))
 	result = tk.MustQuery(`select week("2008-02-20", 5), week("2008-02-20", 6), week("2009-02-20", 7), week("2008-02-20", 8), week("2008-02-20", 9);`)
 	result.Check(testkit.Rows("7 8 7 7 8"))
+	result = tk.MustQuery(`select week("2023-01-01", null);`)
+	result.Check(testkit.Rows("1"))
+	tk.MustQuery("show warnings").Check(testkit.Rows())
 	result = tk.MustQuery(`select week("aa", 1), week(null, 2), week(11, 2), week(12.99, 2);`)
 	result.Check(testkit.Rows("<nil> <nil> <nil> <nil>"))
 	result = tk.MustQuery(`select week("aa"), week(null), week(11), week(12.99);`)