executor: avoid sum from avg overflow

executor/aggfuncs/aggfuncs.go

@@ -188,9 +188,8 @@ type baseAggFunc struct {
 	// used to append the final result of this function.
 	ordinal int
 
-	// frac stores digits of the fractional part of decimals,
-	// which makes the decimal be the result of type inferring.
-	frac int
+	// retTp means the target type of the final agg should return.
+	retTp *types.FieldType
 }
 
 func (*baseAggFunc) MergePartialResult(sctx sessionctx.Context, src, dst PartialResult) (memDelta int64, err error) {

executor/aggfuncs/builder.go

@@ -18,7 +18,6 @@ import (
 	"fmt"
 	"strconv"
 
-	"github.com/cznic/mathutil"
 	"github.com/pingcap/tidb/expression"
 	"github.com/pingcap/tidb/expression/aggregation"
 	"github.com/pingcap/tidb/parser/ast"
@@ -194,6 +193,7 @@ func buildCount(aggFuncDesc *aggregation.AggFuncDesc, ordinal int) AggFunc {
 	base := baseAggFunc{
 		args:    aggFuncDesc.Args,
 		ordinal: ordinal,
+		retTp:   aggFuncDesc.RetTp,
 	}
 
 	// If HasDistinct and mode is CompleteMode or Partial1Mode, we should
@@ -253,13 +253,9 @@ func buildSum(ctx sessionctx.Context, aggFuncDesc *aggregation.AggFuncDesc, ordi
 		baseAggFunc: baseAggFunc{
 			args:    aggFuncDesc.Args,
 			ordinal: ordinal,
+			retTp:   aggFuncDesc.RetTp,
 		},
 	}
-	frac := base.args[0].GetType().Decimal
-	if frac == -1 {
-		frac = mysql.MaxDecimalScale
-	}
-	base.frac = mathutil.Min(frac, mysql.MaxDecimalScale)
 	switch aggFuncDesc.Mode {
 	case aggregation.DedupMode:
 		return nil
@@ -287,16 +283,8 @@ func buildAvg(ctx sessionctx.Context, aggFuncDesc *aggregation.AggFuncDesc, ordi
 	base := baseAggFunc{
 		args:    aggFuncDesc.Args,
 		ordinal: ordinal,
+		retTp:   aggFuncDesc.RetTp,
 	}
-	frac := base.args[0].GetType().Decimal
-	if len(base.args) == 2 {
-		frac = base.args[1].GetType().Decimal
-	}
-	if frac == -1 {
-		frac = mysql.MaxDecimalScale
-	}
-	base.frac = mathutil.Min(frac, mysql.MaxDecimalScale)
-
 	switch aggFuncDesc.Mode {
 	// Build avg functions which consume the original data and remove the
 	// duplicated input of the same group.
@@ -340,13 +328,8 @@ func buildFirstRow(aggFuncDesc *aggregation.AggFuncDesc, ordinal int) AggFunc {
 	base := baseAggFunc{
 		args:    aggFuncDesc.Args,
 		ordinal: ordinal,
+		retTp:   aggFuncDesc.RetTp,
 	}
-	frac := base.args[0].GetType().Decimal
-	if frac == -1 {
-		frac = mysql.MaxDecimalScale
-	}
-	base.frac = mathutil.Min(frac, mysql.MaxDecimalScale)
-
 	evalType, fieldType := aggFuncDesc.RetTp.EvalType(), aggFuncDesc.RetTp
 	if fieldType.Tp == mysql.TypeBit {
 		evalType = types.ETString
@@ -392,15 +375,10 @@ func buildMaxMin(aggFuncDesc *aggregation.AggFuncDesc, ordinal int, isMax bool)
 		baseAggFunc: baseAggFunc{
 			args:    aggFuncDesc.Args,
 			ordinal: ordinal,
+			retTp:   aggFuncDesc.RetTp,
 		},
 		isMax: isMax,
 	}
-	frac := base.args[0].GetType().Decimal
-	if frac == -1 {
-		frac = mysql.MaxDecimalScale
-	}
-	base.frac = mathutil.Min(frac, mysql.MaxDecimalScale)
-
 	evalType, fieldType := aggFuncDesc.RetTp.EvalType(), aggFuncDesc.RetTp
 	if fieldType.Tp == mysql.TypeBit {
 		evalType = types.ETString

executor/aggfuncs/func_avg.go

@@ -17,6 +17,8 @@ package aggfuncs
 import (
 	"unsafe"
 
+	"github.com/pingcap/errors"
+	"github.com/pingcap/tidb/parser/mysql"
 	"github.com/pingcap/tidb/sessionctx"
 	"github.com/pingcap/tidb/types"
 	"github.com/pingcap/tidb/util/chunk"
@@ -72,7 +74,14 @@ func (e *baseAvgDecimal) AppendFinalResult2Chunk(sctx sessionctx.Context, pr Par
 	if err != nil {
 		return err
 	}
-	err = finalResult.Round(finalResult, e.frac, types.ModeHalfEven)
+	if e.retTp == nil {
+		return errors.New("e.retTp of avg should not be nil")
+	}
+	frac := e.retTp.Decimal
+	if frac == -1 {
+		frac = mysql.MaxDecimalScale
+	}
+	err = finalResult.Round(finalResult, frac, types.ModeHalfEven)
 	if err != nil {
 		return err
 	}
@@ -260,7 +269,14 @@ func (e *avgOriginal4DistinctDecimal) AppendFinalResult2Chunk(sctx sessionctx.Co
 	if err != nil {
 		return err
 	}
-	err = finalResult.Round(finalResult, e.frac, types.ModeHalfEven)
+	if e.retTp == nil {
+		return errors.New("e.retTp of avg should not be nil")
+	}
+	frac := e.retTp.Decimal
+	if frac == -1 {
+		frac = mysql.MaxDecimalScale
+	}
+	err = finalResult.Round(finalResult, frac, types.ModeHalfEven)
 	if err != nil {
 		return err
 	}

executor/aggfuncs/func_first_row.go

@@ -17,6 +17,8 @@ package aggfuncs
 import (
 	"unsafe"
 
+	"github.com/pingcap/errors"
+	"github.com/pingcap/tidb/parser/mysql"
 	"github.com/pingcap/tidb/sessionctx"
 	"github.com/pingcap/tidb/types"
 	"github.com/pingcap/tidb/types/json"
@@ -476,7 +478,14 @@ func (e *firstRow4Decimal) AppendFinalResult2Chunk(sctx sessionctx.Context, pr P
 		chk.AppendNull(e.ordinal)
 		return nil
 	}
-	err := p.val.Round(&p.val, e.frac, types.ModeHalfEven)
+	if e.retTp == nil {
+		return errors.New("e.retTp of first_row should not be nil")
+	}
+	frac := e.retTp.Decimal
+	if frac == -1 {
+		frac = mysql.MaxDecimalScale
+	}
+	err := p.val.Round(&p.val, frac, types.ModeHalfEven)
 	if err != nil {
 		return err
 	}

executor/aggfuncs/func_max_min.go

@@ -18,6 +18,7 @@ import (
 	"unsafe"
 
 	"github.com/pingcap/errors"
+	"github.com/pingcap/tidb/parser/mysql"
 	"github.com/pingcap/tidb/sessionctx"
 	"github.com/pingcap/tidb/types"
 	"github.com/pingcap/tidb/types/json"
@@ -812,7 +813,14 @@ func (e *maxMin4Decimal) AppendFinalResult2Chunk(sctx sessionctx.Context, pr Par
 		chk.AppendNull(e.ordinal)
 		return nil
 	}
-	err := p.val.Round(&p.val, e.frac, types.ModeHalfEven)
+	if e.retTp == nil {
+		return errors.New("e.retTp of max or min should not be nil")
+	}
+	frac := e.retTp.Decimal
+	if frac == -1 {
+		frac = mysql.MaxDecimalScale
+	}
+	err := p.val.Round(&p.val, frac, types.ModeHalfEven)
 	if err != nil {
 		return err
 	}

executor/aggfuncs/func_sum.go

@@ -17,6 +17,8 @@ package aggfuncs
 import (
 	"unsafe"
 
+	"github.com/pingcap/errors"
+	"github.com/pingcap/tidb/parser/mysql"
 	"github.com/pingcap/tidb/sessionctx"
 	"github.com/pingcap/tidb/types"
 	"github.com/pingcap/tidb/util/chunk"
@@ -169,7 +171,14 @@ func (e *sum4Decimal) AppendFinalResult2Chunk(sctx sessionctx.Context, pr Partia
 		chk.AppendNull(e.ordinal)
 		return nil
 	}
-	err := p.val.Round(&p.val, e.frac, types.ModeHalfEven)
+	if e.retTp == nil {
+		return errors.New("e.retTp of sum should not be nil")
+	}
+	frac := e.retTp.Decimal
+	if frac == -1 {
+		frac = mysql.MaxDecimalScale
+	}
+	err := p.val.Round(&p.val, frac, types.ModeHalfEven)
 	if err != nil {
 		return err
 	}

executor/aggregate_test.go

@@ -1494,6 +1494,28 @@ func TestIssue23277(t *testing.T) {
 	tk.MustExec("drop table t;")
 }
 
+func TestAvgDecimal(t *testing.T) {
+	t.Parallel()
+	store, clean := testkit.CreateMockStore(t)
+	defer clean()
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test;")
+	tk.MustExec("drop table if exists td;")
+	tk.MustExec("create table td (col_bigint bigint(20), col_smallint smallint(6));")
+	tk.MustExec("insert into td values (null, 22876);")
+	tk.MustExec("insert into td values (9220557287087669248, 32767);")
+	tk.MustExec("insert into td values (28030, 32767);")
+	tk.MustExec("insert into td values (-3309864251140603904,32767);")
+	tk.MustExec("insert into td values (4,0);")
+	tk.MustExec("insert into td values (null,0);")
+	tk.MustExec("insert into td values (4,-23828);")
+	tk.MustExec("insert into td values (54720,32767);")
+	tk.MustExec("insert into td values (0,29815);")
+	tk.MustExec("insert into td values (10017,-32661);")
+	tk.MustQuery(" SELECT AVG( col_bigint / col_smallint) AS field1 FROM td;").Sort().Check(testkit.Rows("25769363061037.62077260"))
+	tk.MustExec("drop table td;")
+}
+
 // https://github.com/pingcap/tidb/issues/23314
 func TestIssue23314(t *testing.T) {
 	t.Parallel()

executor/tiflash_test.go

@@ -790,6 +790,48 @@ func (s *tiflashTestSuite) TestUnionWithEmptyDualTable(c *C) {
 	tk.MustQuery("select count(*) from (select a , b from t union all select a , c from t1 where false) tt").Check(testkit.Rows("1"))
 }
 
+func (s *tiflashTestSuite) TestAvgOverflow(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+	// avg int
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t (a decimal(1,0))")
+	tk.MustExec("alter table t set tiflash replica 1")
+	tb := testGetTableByName(c, tk.Se, "test", "t")
+	err := domain.GetDomain(tk.Se).DDL().UpdateTableReplicaInfo(tk.Se, tb.Meta().ID, true)
+	c.Assert(err, IsNil)
+	tk.MustExec("insert into t values(9)")
+	for i := 0; i < 16; i++ {
+		tk.MustExec("insert into t select * from t")
+	}
+	tk.MustExec("set @@session.tidb_isolation_read_engines=\"tiflash\"")
+	tk.MustExec("set @@session.tidb_enforce_mpp=ON")
+	tk.MustQuery("select avg(a) from t group by a").Check(testkit.Rows("9.0000"))
+	tk.MustExec("drop table if exists t")
+
+	// avg decimal
+	tk.MustExec("drop table if exists td;")
+	tk.MustExec("create table td (col_bigint bigint(20), col_smallint smallint(6));")
+	tk.MustExec("alter table td set tiflash replica 1")
+	tb = testGetTableByName(c, tk.Se, "test", "td")
+	err = domain.GetDomain(tk.Se).DDL().UpdateTableReplicaInfo(tk.Se, tb.Meta().ID, true)
+	c.Assert(err, IsNil)
+	tk.MustExec("insert into td values (null, 22876);")
+	tk.MustExec("insert into td values (9220557287087669248, 32767);")
+	tk.MustExec("insert into td values (28030, 32767);")
+	tk.MustExec("insert into td values (-3309864251140603904,32767);")
+	tk.MustExec("insert into td values (4,0);")
+	tk.MustExec("insert into td values (null,0);")
+	tk.MustExec("insert into td values (4,-23828);")
+	tk.MustExec("insert into td values (54720,32767);")
+	tk.MustExec("insert into td values (0,29815);")
+	tk.MustExec("insert into td values (10017,-32661);")
+	tk.MustExec("set @@session.tidb_isolation_read_engines=\"tiflash\"")
+	tk.MustExec("set @@session.tidb_enforce_mpp=ON")
+	tk.MustQuery(" SELECT AVG( col_bigint / col_smallint) AS field1 FROM td;").Sort().Check(testkit.Rows("25769363061037.62077260"))
+	tk.MustExec("drop table if exists td;")
+}
+
 func (s *tiflashTestSuite) TestMppApply(c *C) {
 	tk := testkit.NewTestKit(c, s.store)
 	tk.MustExec("use test")

expression/aggregation/base_func.go

@@ -43,7 +43,7 @@ type baseFuncDesc struct {
 
 func newBaseFuncDesc(ctx sessionctx.Context, name string, args []expression.Expression) (baseFuncDesc, error) {
 	b := baseFuncDesc{Name: strings.ToLower(name), Args: args}
-	err := b.typeInfer(ctx)
+	err := b.TypeInfer(ctx)
 	return b, err
 }
 
@@ -84,8 +84,8 @@ func (a *baseFuncDesc) String() string {
 	return buffer.String()
 }
 
-// typeInfer infers the arguments and return types of an function.
-func (a *baseFuncDesc) typeInfer(ctx sessionctx.Context) error {
+// TypeInfer infers the arguments and return types of an function.
+func (a *baseFuncDesc) TypeInfer(ctx sessionctx.Context) error {
 	switch a.Name {
 	case ast.AggFuncCount:
 		a.typeInfer4Count(ctx)
@@ -207,6 +207,14 @@ func (a *baseFuncDesc) typeInfer4Sum(ctx sessionctx.Context) {
 	types.SetBinChsClnFlag(a.RetTp)
 }
 
+// TypeInfer4AvgSum infers the type of sum from avg, which should extend the precision of decimal
+// compatible with mysql.
+func (a *baseFuncDesc) TypeInfer4AvgSum(avgRetType *types.FieldType) {
+	if avgRetType.Tp == mysql.TypeNewDecimal {
+		a.RetTp.Flen = mathutil.Min(mysql.MaxDecimalWidth, a.RetTp.Flen+22)
+	}
+}
+
 // typeInfer4Avg should returns a "decimal", otherwise it returns a "double".
 // Because child returns integer or decimal type.
 func (a *baseFuncDesc) typeInfer4Avg(ctx sessionctx.Context) {
@@ -246,6 +254,12 @@ func (a *baseFuncDesc) typeInfer4GroupConcat(ctx sessionctx.Context) {
 
 	a.RetTp.Flen, a.RetTp.Decimal = mysql.MaxBlobWidth, 0
 	// TODO: a.Args[i] = expression.WrapWithCastAsString(ctx, a.Args[i])
+	for i := 0; i < len(a.Args)-1; i++ {
+		if tp := a.Args[i].GetType(); tp.Tp == mysql.TypeNewDecimal {
+			a.Args[i] = expression.BuildCastFunction(ctx, a.Args[i], tp)
+		}
+	}
+
 }
 
 func (a *baseFuncDesc) typeInfer4MaxMin(ctx sessionctx.Context) {
@@ -370,18 +384,6 @@ var noNeedCastAggFuncs = map[string]struct{}{
 	ast.AggFuncJsonObjectAgg:       {},
 }
 
-// WrapCastAsDecimalForAggArgs wraps the args of some specific aggregate functions
-// with a cast as decimal function. See issue #19426
-func (a *baseFuncDesc) WrapCastAsDecimalForAggArgs(ctx sessionctx.Context) {
-	if a.Name == ast.AggFuncGroupConcat {
-		for i := 0; i < len(a.Args)-1; i++ {
-			if tp := a.Args[i].GetType(); tp.Tp == mysql.TypeNewDecimal {
-				a.Args[i] = expression.BuildCastFunction(ctx, a.Args[i], tp)
-			}
-		}
-	}
-}
-
 // WrapCastForAggArgs wraps the args of an aggregate function with a cast function.
 func (a *baseFuncDesc) WrapCastForAggArgs(ctx sessionctx.Context) {
 	if len(a.Args) == 0 {

planner/core/rule_inject_extra_projection.go

@@ -106,7 +106,6 @@ func injectProjBelowUnion(un *PhysicalUnionAll) *PhysicalUnionAll {
 // since the types of the args are already the expected.
 func wrapCastForAggFuncs(sctx sessionctx.Context, aggFuncs []*aggregation.AggFuncDesc) {
 	for i := range aggFuncs {
-		aggFuncs[i].WrapCastAsDecimalForAggArgs(sctx)
 		if aggFuncs[i].Mode != aggregation.FinalMode && aggFuncs[i].Mode != aggregation.Partial2Mode {
 			aggFuncs[i].WrapCastForAggArgs(sctx)
 		}