56 lines
1.5 KiB
Go
56 lines
1.5 KiB
Go
// Copyright 2016 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 expression
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import (
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"github.com/ngaut/log"
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"github.com/pingcap/tidb/context"
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"github.com/pingcap/tidb/util/types"
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)
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// FoldConstant does constant folding optimization on an expression.
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func FoldConstant(ctx context.Context, expr Expression) Expression {
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scalarFunc, ok := expr.(*ScalarFunction)
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if !ok {
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return expr
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}
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if _, isDynamic := DynamicFuncs[scalarFunc.FuncName.L]; isDynamic {
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return expr
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}
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args := scalarFunc.GetArgs()
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datums := make([]types.Datum, 0, len(args))
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canFold := true
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for i := 0; i < len(args); i++ {
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foldedArg := FoldConstant(ctx, args[i])
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scalarFunc.GetArgs()[i] = foldedArg
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if con, ok := foldedArg.(*Constant); ok {
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datums = append(datums, con.Value)
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} else {
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canFold = false
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}
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}
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if !canFold {
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return expr
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}
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value, err := scalarFunc.Function(datums, ctx)
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if err != nil {
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log.Warnf("There may exist an error during constant folding. The function name is %s, args are %s", scalarFunc.FuncName, args)
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return expr
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}
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return &Constant{
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Value: value,
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RetType: scalarFunc.RetType,
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}
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}
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