planner: do not eliminate group_concat in aggregate elimination #9967
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zz-jason
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Apr 1, 2019
zz-jason
reviewed
Apr 1, 2019
zz-jason
changed the title
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/run-all-tests |
winoros
reviewed
Apr 1, 2019
| @@ -36,6 +36,19 @@ type aggregationEliminateChecker struct { | |||
| // For count(expr), sum(expr), avg(expr), count(distinct expr, [expr...]) we may need to rewrite the expr. Details are shown below. | |||
| // If we can eliminate agg successful, we return a projection. Else we return a nil pointer. | |||
| func (a *aggregationEliminateChecker) tryToEliminateAggregation(agg *LogicalAggregation) *LogicalProjection { | |||
| for _, af := range agg.AggFuncs { | |||
| // TODO: Actually, we can rewrite GROUP_CONCAT. | |||
| // When it accepts only 1 argument, we can extract this argument into a | |||
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This case is easy to be added in this pr?
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Noop, since group_concat_max_len is configurable.
We can not ensure whether the length of the final result exceeds max_len even if there is only 1 argument.
And, maybe it'll be easier to implement if we wrap the argument(s) into a concat_ws despite the count of the arguments.
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/run-all-tests |
Codecov Report
@@ Coverage Diff @@
## master #9967 +/- ##
================================================
+ Coverage 77.4704% 77.4772% +0.0067%
================================================
Files 403 404 +1
Lines 81777 81775 -2
================================================
+ Hits 63353 63357 +4
+ Misses 13707 13704 -3
+ Partials 4717 4714 -3 |
eurekaka
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status/LGT2
|
/run-unit-test |
zz-jason
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Apr 1, 2019
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What problem does this PR solve?
fix #9922
What is changed and how it works?
Do not eliminate group_concat considering system variable group_concat_max_len.
Actually, we can rewrite GROUP_CONCAT when all the arguments it
accepts are promised to be NOT-NULL. (Recorded as a task in #9968)
When it accepts only 1 argument, we can extract this argument into a
projection.
When it accepts multiple arguments, we can wrap the arguments with a
function CONCAT_WS and extract this function into a projection.
BUT, GROUP_CONCAT should truncate the final result according to the
system variable
group_concat_max_len. To ensure the correctness ofthe result, we close the elimination of GROUP_CONCAT here.
Check List
Tests
Code changes
Side effects
Performance may regress when group_concat accepts only 1 argument.
Related changes