executor: add window function NTILE

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.WindowFuncNtile:
+		return buildNtile(windowFuncDesc, ordinal)
 	default:
 		return Build(ctx, windowFuncDesc, ordinal)
 	}
@@ -386,3 +388,12 @@ func buildNthValue(aggFuncDesc *aggregation.AggFuncDesc, ordinal int) AggFunc {
 	nth, _, _ := expression.GetUint64FromConstant(aggFuncDesc.Args[1])
 	return &nthValue{baseAggFunc: base, tp: aggFuncDesc.RetTp, nth: nth}
 }
+
+func buildNtile(aggFuncDes *aggregation.AggFuncDesc, ordinal int) AggFunc {
+	base := baseAggFunc{
+		args:    aggFuncDes.Args,
+		ordinal: ordinal,
+	}
+	n, _, _ := expression.GetUint64FromConstant(aggFuncDes.Args[0])
+	return &ntile{baseAggFunc: base, n: n}
+}

executor/aggfuncs/func_ntile.go

@@ -0,0 +1,81 @@
+// 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"
+)
+
+// ntile divides the partition into n ranked groups and returns the group number a row belongs to.
+// e.g. We have 11 rows and n = 3. They will be divided into 3 groups.
+//      First 4 rows belongs to group 1. Following 4 rows belongs to group 2. The last 3 rows belongs to group 3.
+type ntile struct {
+	n uint64
+	baseAggFunc
+}
+
+type partialResult4Ntile struct {
+	curIdx      uint64
+	divisor     uint64
+	curGroupIdx uint64
+	remainder   uint64
+	quotient    uint64
+	rows        []chunk.Row
+}
+
+func (n *ntile) AllocPartialResult() PartialResult {
+	return PartialResult(&partialResult4Ntile{divisor: n.n, curGroupIdx: 1})
+}
+
+func (n *ntile) ResetPartialResult(pr PartialResult) {
+	p := (*partialResult4Ntile)(pr)
+	p.curIdx = 0
+	p.curGroupIdx = 1
+	p.rows = p.rows[:0]
+}
+
+func (n *ntile) UpdatePartialResult(_ sessionctx.Context, rowsInGroup []chunk.Row, pr PartialResult) error {
+	p := (*partialResult4Ntile)(pr)
+	p.rows = append(p.rows, rowsInGroup...)
+	// Update the quotient and remainder.
+	if p.divisor != 0 {
+		p.quotient = uint64(len(p.rows)) / p.divisor
+		p.remainder = uint64(len(p.rows)) % p.divisor
+	}
+	return nil
+}
+
+func (n *ntile) AppendFinalResult2Chunk(_ sessionctx.Context, pr PartialResult, chk *chunk.Chunk) error {
+	p := (*partialResult4Ntile)(pr)
+
+	// If the divisor is 0, the arg of NTILE would be NULL. So we just return NULL.
+	if p.divisor == 0 {
+		chk.AppendNull(n.ordinal)
+		return nil
+	}
+
+	chk.AppendUint64(n.ordinal, p.curGroupIdx)
+
+	p.curIdx++
+	curMaxIdx := p.quotient
+	if p.curGroupIdx <= p.remainder {
+		curMaxIdx++
+	}
+	if p.curIdx == curMaxIdx {
+		p.curIdx = 0
+		p.curGroupIdx++
+	}
+	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 ntile(3) over() from t")
+	result.Check(testkit.Rows("1", "1", "2", "3"))
+	result = tk.MustQuery("select ntile(2) over() from t")
+	result.Check(testkit.Rows("1", "1", "2", "2"))
+	result = tk.MustQuery("select ntile(null) over() from t")
+	result.Check(testkit.Rows("<nil>", "<nil>", "<nil>", "<nil>"))
 }

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.WindowFuncNtile:
+		a.typeInfer4Ntile()
 	default:
 		panic("unsupported agg function: " + a.Name)
 	}
@@ -200,6 +202,13 @@ func (a *baseFuncDesc) typeInfer4CumeDist() {
 	a.RetTp.Flen, a.RetTp.Decimal = mysql.MaxRealWidth, mysql.NotFixedDec
 }
 
+func (a *baseFuncDesc) typeInfer4Ntile() {
+	a.RetTp = types.NewFieldType(mysql.TypeLonglong)
+	a.RetTp.Flen = 21
+	types.SetBinChsClnFlag(a.RetTp)
+	a.RetTp.Flag |= mysql.UnsignedFlag
+}
+
 // 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.

expression/aggregation/window_func.go

@@ -28,12 +28,19 @@ type WindowFuncDesc struct {
 
 // NewWindowFuncDesc creates a window function signature descriptor.
 func NewWindowFuncDesc(ctx sessionctx.Context, name string, args []expression.Expression) *WindowFuncDesc {
-	if strings.ToLower(name) == ast.WindowFuncNthValue {
+	switch strings.ToLower(name) {
+	case ast.WindowFuncNthValue:
 		val, isNull, ok := expression.GetUint64FromConstant(args[1])
 		// nth_value does not allow `0`, but allows `null`.
 		if !ok || (val == 0 && !isNull) {
 			return nil
 		}
+	case ast.WindowFuncNtile:
+		val, isNull, ok := expression.GetUint64FromConstant(args[0])
+		// ntile does not allow `0`, but allows `null`.
+		if !ok || (val == 0 && !isNull) {
+			return nil
+		}
 	}
 	return &WindowFuncDesc{newBaseFuncDesc(ctx, name, args)}
 }

planner/core/logical_plan_test.go

@@ -2207,6 +2207,14 @@ func (s *testPlanSuite) TestWindowFunction(c *C) {
 			sql:    "select nth_value(a, 0) over() from t",
 			result: "[planner:1210]Incorrect arguments to nth_value",
 		},
+		{
+			sql:    "select ntile(0) over() from t",
+			result: "[planner:1210]Incorrect arguments to ntile",
+		},
+		{
+			sql:    "select ntile(null) over() from t",
+			result: "TableReader(Table(t))->Window(ntile(<nil>) over())->Projection",
+		},
 	}
 
 	s.Parser.EnableWindowFunc(true)