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81 lines
2.1 KiB
81 lines
2.1 KiB
// Copyright 2019 PingCAP, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package aggfuncs
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import (
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"github.com/pingcap/tidb/sessionctx"
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"github.com/pingcap/tidb/util/chunk"
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)
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// ntile divides the partition into n ranked groups and returns the group number a row belongs to.
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// e.g. We have 11 rows and n = 3. They will be divided into 3 groups.
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//
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// First 4 rows belongs to group 1. Following 4 rows belongs to group 2. The last 3 rows belongs to group 3.
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type ntile struct {
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n uint64
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baseAggFunc
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}
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type partialResult4Ntile struct {
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curIdx uint64
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curGroupIdx uint64
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remainder uint64
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quotient uint64
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numRows uint64
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}
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func (n *ntile) AllocPartialResult() PartialResult {
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return PartialResult(&partialResult4Ntile{curGroupIdx: 1})
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}
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func (n *ntile) ResetPartialResult(pr PartialResult) {
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p := (*partialResult4Ntile)(pr)
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p.curIdx = 0
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p.curGroupIdx = 1
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p.numRows = 0
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}
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func (n *ntile) UpdatePartialResult(_ sessionctx.Context, rowsInGroup []chunk.Row, pr PartialResult) error {
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p := (*partialResult4Ntile)(pr)
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p.numRows += uint64(len(rowsInGroup))
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// Update the quotient and remainder.
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if n.n != 0 {
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p.quotient = p.numRows / n.n
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p.remainder = p.numRows % n.n
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}
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return nil
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}
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func (n *ntile) AppendFinalResult2Chunk(_ sessionctx.Context, pr PartialResult, chk *chunk.Chunk) error {
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p := (*partialResult4Ntile)(pr)
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// If the divisor is 0, the arg of NTILE would be NULL. So we just return NULL.
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if n.n == 0 {
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chk.AppendNull(n.ordinal)
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return nil
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}
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chk.AppendUint64(n.ordinal, p.curGroupIdx)
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p.curIdx++
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curMaxIdx := p.quotient
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if p.curGroupIdx <= p.remainder {
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curMaxIdx++
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}
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if p.curIdx == curMaxIdx {
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p.curIdx = 0
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p.curGroupIdx++
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}
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return nil
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}
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