executor: add window function PERCENT_RANK (#9671)

executor/aggfuncs/builder.go

@@ -73,6 +73,8 @@ func BuildWindowFunctions(ctx sessionctx.Context, windowFuncDesc *aggregation.Ag
 		return buildCumeDist(ordinal, orderByCols)
 	case ast.WindowFuncNthValue:
 		return buildNthValue(windowFuncDesc, ordinal)
+	case ast.WindowFuncPercentRank:
+		return buildPercenRank(ordinal, orderByCols)
 	default:
 		return Build(ctx, windowFuncDesc, ordinal)
 	}
@@ -386,3 +388,10 @@ func buildNthValue(aggFuncDesc *aggregation.AggFuncDesc, ordinal int) AggFunc {
 	nth, _, _ := expression.GetUint64FromConstant(aggFuncDesc.Args[1])
 	return &nthValue{baseAggFunc: base, tp: aggFuncDesc.RetTp, nth: nth}
 }
+
+func buildPercenRank(ordinal int, orderByCols []*expression.Column) AggFunc {
+	base := baseAggFunc{
+		ordinal: ordinal,
+	}
+	return &percentRank{baseAggFunc: base, rowComparer: buildRowComparer(orderByCols)}
+}

executor/aggfuncs/func_percent_rank.go

@@ -0,0 +1,61 @@
+// Copyright 2019 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package aggfuncs
+
+import (
+	"github.com/pingcap/tidb/sessionctx"
+	"github.com/pingcap/tidb/util/chunk"
+)
+
+// percentRank calculates the percentage of partition values less than the value in the current row, excluding the highest value.
+// It can be calculated as `(rank - 1) / (total_rows_in_set - 1).
+type percentRank struct {
+	baseAggFunc
+	rowComparer
+}
+
+func (pr *percentRank) AllocPartialResult() PartialResult {
+	return PartialResult(&partialResult4Rank{})
+}
+
+func (pr *percentRank) ResetPartialResult(partial PartialResult) {
+	p := (*partialResult4Rank)(partial)
+	p.curIdx = 0
+	p.lastRank = 0
+	p.rows = p.rows[:0]
+}
+
+func (pr *percentRank) UpdatePartialResult(sctx sessionctx.Context, rowsInGroup []chunk.Row, partial PartialResult) error {
+	p := (*partialResult4Rank)(partial)
+	p.rows = append(p.rows, rowsInGroup...)
+	return nil
+}
+
+func (pr *percentRank) AppendFinalResult2Chunk(sctx sessionctx.Context, partial PartialResult, chk *chunk.Chunk) error {
+	p := (*partialResult4Rank)(partial)
+	numRows := int64(len(p.rows))
+	p.curIdx++
+	if p.curIdx == 1 {
+		p.lastRank = 1
+		chk.AppendFloat64(pr.ordinal, 0)
+		return nil
+	}
+	if pr.compareRows(p.rows[p.curIdx-2], p.rows[p.curIdx-1]) == 0 {
+		chk.AppendFloat64(pr.ordinal, float64(p.lastRank-1)/float64(numRows-1))
+		return nil
+	}
+	p.lastRank = p.curIdx
+	chk.AppendFloat64(pr.ordinal, float64(p.lastRank-1)/float64(numRows-1))
+	return nil
+}

executor/window_test.go

@@ -119,4 +119,11 @@ func (s *testSuite2) TestWindowFunctions(c *C) {
 	result.Check(testkit.Rows("1 2", "1 2", "2 2", "2 2"))
 	result = tk.MustQuery("select a, nth_value(a, 5) over() from t")
 	result.Check(testkit.Rows("1 <nil>", "1 <nil>", "2 <nil>", "2 <nil>"))
+
+	result = tk.MustQuery("select a, percent_rank() over() from t")
+	result.Check(testkit.Rows("1 0", "1 0", "2 0", "2 0"))
+	result = tk.MustQuery("select a, percent_rank() over(order by a) from t")
+	result.Check(testkit.Rows("1 0", "1 0", "2 0.6666666666666666", "2 0.6666666666666666"))
+	result = tk.MustQuery("select a, b, percent_rank() over(order by a, b) from t")
+	result.Check(testkit.Rows("1 1 0", "1 2 0.3333333333333333", "2 1 0.6666666666666666", "2 2 1"))
 }

expression/aggregation/base_func.go

@@ -100,6 +100,8 @@ func (a *baseFuncDesc) typeInfer(ctx sessionctx.Context) {
 		a.typeInfer4NumberFuncs()
 	case ast.WindowFuncCumeDist:
 		a.typeInfer4CumeDist()
+	case ast.WindowFuncPercentRank:
+		a.typeInfer4PercentRank()
 	default:
 		panic("unsupported agg function: " + a.Name)
 	}
@@ -200,6 +202,11 @@ func (a *baseFuncDesc) typeInfer4CumeDist() {
 	a.RetTp.Flen, a.RetTp.Decimal = mysql.MaxRealWidth, mysql.NotFixedDec
 }
 
+func (a *baseFuncDesc) typeInfer4PercentRank() {
+	a.RetTp = types.NewFieldType(mysql.TypeDouble)
+	a.RetTp.Flag, a.RetTp.Decimal = mysql.MaxRealWidth, mysql.NotFixedDec
+}
+
 // GetDefaultValue gets the default value when the function's input is null.
 // According to MySQL, default values of the function are listed as follows:
 // e.g.