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plan: fix predicate push down for UnionScan #7695

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merged 4 commits into from
Sep 17, 2018
Merged

plan: fix predicate push down for UnionScan #7695

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3b197b7
plan: fix predicate push down for UnionScan
coocood Sep 14, 2018
3f6b79a
add explain test
coocood Sep 14, 2018
70ba25a
Merge branch 'master' into fix-union-scan
shenli Sep 17, 2018
daff36a
Merge branch 'master' into fix-union-scan
winoros Sep 17, 2018
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13 changes: 13 additions & 0 deletions cmd/explaintest/r/explain_easy.result
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Original file line number Diff line number Diff line change
Expand Up @@ -352,3 +352,16 @@ create table t(a bigint primary key);
explain select * from t where a = 1 and a = 2;
id count task operator info
TableDual_5 0.00 root rows:0
drop table if exists ta, tb;
create table ta (a varchar(20));
create table tb (a varchar(20));
begin;
insert tb values ('1');
explain select * from ta where a = 1;
id count task operator info
Projection_5 8000.00 root test.ta.a
└─Selection_6 8000.00 root eq(cast(test.ta.a), 1)
└─UnionScan_7 10000.00 root eq(cast(test.ta.a), 1)
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why not Eval it in getSnapshotRow?

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It's out of the scope of UnionScan's responsibility

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Then why not removing all the filters inside the UnionScan?

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It can be refactored later.

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The filter a = 1, which is Selection_6, should be added as a parent of TableReader_9.

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This is better, we can do it in the next PR.

└─TableReader_9 10000.00 root data:TableScan_8
└─TableScan_8 10000.00 cop table:ta, range:[-inf,+inf], keep order:false, stats:pseudo
rollback;
8 changes: 8 additions & 0 deletions cmd/explaintest/t/explain_easy.test
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Expand Up @@ -70,3 +70,11 @@ explain select * from t where b = 1 and b = 2;
drop table if exists t;
create table t(a bigint primary key);
explain select * from t where a = 1 and a = 2;

drop table if exists ta, tb;
create table ta (a varchar(20));
create table tb (a varchar(20));
begin;
insert tb values ('1');
explain select * from ta where a = 1;
rollback;
13 changes: 13 additions & 0 deletions executor/union_scan_test.go
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Expand Up @@ -78,3 +78,16 @@ func (s *testSuite) TestDirtyTransaction(c *C) {
tk.MustQuery("select * from t use index(idx) where c > 1 and d = 4").Check(testkit.Rows("1 2 3 4"))
tk.MustExec("commit")
}

func (s *testSuite) TestUnionScanWithCastCondition(c *C) {
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It's better to add another explain test.

tk := testkit.NewTestKit(c, s.store)
tk.MustExec("use test")
tk.MustExec("create table ta (a varchar(20))")
tk.MustExec("insert ta values ('1'), ('2')")
tk.MustExec("create table tb (a varchar(20))")
tk.MustExec("begin")
tk.MustQuery("select * from ta where a = 1").Check(testkit.Rows("1"))
tk.MustExec("insert tb values ('0')")
tk.MustQuery("select * from ta where a = 1").Check(testkit.Rows("1"))
tk.MustExec("rollback")
}
5 changes: 3 additions & 2 deletions plan/rule_predicate_push_down.go
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Expand Up @@ -62,12 +62,13 @@ func (p *LogicalSelection) PredicatePushDown(predicates []expression.Expression)

// PredicatePushDown implements LogicalPlan PredicatePushDown interface.
func (p *LogicalUnionScan) PredicatePushDown(predicates []expression.Expression) ([]expression.Expression, LogicalPlan) {
p.children[0].PredicatePushDown(predicates)
retainedPredicates, _ := p.children[0].PredicatePushDown(predicates)
p.conditions = make([]expression.Expression, 0, len(predicates))
for _, cond := range predicates {
p.conditions = append(p.conditions, cond)
}
return nil, p
// The conditions in UnionScan is only used for added rows, so parent Selection should not be removed.
return retainedPredicates, p
}

// PredicatePushDown implements LogicalPlan PredicatePushDown interface.
Expand Down