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planner: add commemt to explain why we need InjectProjBelowAgg (#16670)

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Feng Liyuan
2020-04-23 11:13:33 +08:00
committed by GitHub
parent 595d64eee6
commit 080bcf2ac5
1 changed files with 4 additions and 3 deletions
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7
planner/core/rule_inject_extra_projection.go
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@ -66,9 +66,10 @@ func wrapCastForAggFuncs(sctx sessionctx.Context, aggFuncs []*aggregation.AggFun
}
}
// InjectProjBelowAgg injects a ProjOperator below AggOperator. If all the args
// of `aggFuncs`, and all the item of `groupByItems` are columns or constants,
// we do not need to build the `proj`.
// InjectProjBelowAgg injects a ProjOperator below AggOperator. So that All
// scalar functions in aggregation may speed up by vectorized evaluation in
// the `proj`. If all the args of `aggFuncs`, and all the item of `groupByItems`
// are columns or constants, we do not need to build the `proj`.
func InjectProjBelowAgg(aggPlan PhysicalPlan, aggFuncs []*aggregation.AggFuncDesc, groupByItems []expression.Expression) PhysicalPlan {
hasScalarFunc := false