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)