planner: remove the limitation that predicates can't be pushed throug…

…h `Projection` on `TableDual` (#51329)

close #50614

pkg/planner/core/logical_plans.go

@@ -1371,9 +1371,13 @@ type LogicalMaxOneRow struct {
 }
 
 // LogicalTableDual represents a dual table plan.
+// Note that sometimes we don't set schema for LogicalTableDual (most notably in buildTableDual()), which means
+// outputting 0/1 row with zero column. This semantic may be different from your expectation sometimes but should not
+// cause any actual problems now.
 type LogicalTableDual struct {
 	logicalSchemaProducer
 
+	// RowCount could only be 0 or 1.
 	RowCount int
 }
 

pkg/planner/core/rule_predicate_push_down.go

@@ -522,11 +522,6 @@ func (p *LogicalProjection) PredicatePushDown(predicates []expression.Expression
 			return predicates, child
 		}
 	}
-	if len(p.children) == 1 {
-		if _, isDual := p.children[0].(*LogicalTableDual); isDual {
-			return predicates, p
-		}
-	}
 	exprCtx := p.SCtx().GetExprCtx()
 	for _, cond := range predicates {
 		substituted, hasFailed, newFilter := expression.ColumnSubstituteImpl(exprCtx, cond, p.Schema(), p.Exprs, true)

tests/integrationtest/r/planner/core/casetest/integration.result

@@ -1781,3 +1781,25 @@ from
 (select 1 as c0) as subq_1;
 c1
 NULL
+use test;
+drop table if exists tt;
+create table tt(a bigint, b bigint, c bigint, d bigint, e bigint, primary key(c,d));
+explain format = brief update tt, (select 1 as c1 ,2 as c2 ,3 as c3, 4 as c4 union all select 2,3,4,5 union all select 3,4,5,6) tmp set tt.a=tmp.c1, tt.b=tmp.c2 where tt.c=tmp.c3 and tt.d=tmp.c4 and (tt.c,tt.d) in ((11,111),(22,222),(33,333),(44,444));
+id	estRows	task	access object	operator info
+Update	N/A	root		N/A
+└─Projection	0.00	root		test.tt.a, test.tt.b, test.tt.c, test.tt.d, test.tt.e, Column#18, Column#19, Column#20, Column#21
+  └─Projection	0.00	root		test.tt.a, test.tt.b, test.tt.c, test.tt.d, test.tt.e, Column#18, Column#19, Column#20, Column#21
+    └─IndexJoin	0.00	root		inner join, inner:TableReader, outer key:Column#20, Column#21, inner key:test.tt.c, test.tt.d, equal cond:eq(Column#20, test.tt.c), eq(Column#21, test.tt.d), other cond:or(or(and(eq(Column#20, 11), eq(test.tt.d, 111)), and(eq(Column#20, 22), eq(test.tt.d, 222))), or(and(eq(Column#20, 33), eq(test.tt.d, 333)), and(eq(Column#20, 44), eq(test.tt.d, 444)))), or(or(and(eq(test.tt.c, 11), eq(Column#21, 111)), and(eq(test.tt.c, 22), eq(Column#21, 222))), or(and(eq(test.tt.c, 33), eq(Column#21, 333)), and(eq(test.tt.c, 44), eq(Column#21, 444))))
+      ├─Union(Build)	0.00	root		
+      │ ├─Projection	0.00	root		Column#6->Column#18, Column#7->Column#19, Column#8->Column#20, Column#9->Column#21
+      │ │ └─Projection	0.00	root		1->Column#6, 2->Column#7, 3->Column#8, 4->Column#9
+      │ │   └─TableDual	0.00	root		rows:0
+      │ ├─Projection	0.00	root		Column#10->Column#18, Column#11->Column#19, Column#12->Column#20, Column#13->Column#21
+      │ │ └─Projection	0.00	root		2->Column#10, 3->Column#11, 4->Column#12, 5->Column#13
+      │ │   └─TableDual	0.00	root		rows:0
+      │ └─Projection	0.00	root		Column#14->Column#18, Column#15->Column#19, Column#16->Column#20, Column#17->Column#21
+      │   └─Projection	0.00	root		3->Column#14, 4->Column#15, 5->Column#16, 6->Column#17
+      │     └─TableDual	0.00	root		rows:0
+      └─TableReader(Probe)	0.00	root		data:Selection
+        └─Selection	0.00	cop[tikv]		or(or(and(eq(test.tt.c, 11), eq(test.tt.d, 111)), and(eq(test.tt.c, 22), eq(test.tt.d, 222))), or(and(eq(test.tt.c, 33), eq(test.tt.d, 333)), and(eq(test.tt.c, 44), eq(test.tt.d, 444)))), or(or(eq(test.tt.c, 11), eq(test.tt.c, 22)), or(eq(test.tt.c, 33), eq(test.tt.c, 44))), or(or(eq(test.tt.d, 111), eq(test.tt.d, 222)), or(eq(test.tt.d, 333), eq(test.tt.d, 444)))
+          └─TableRangeScan	0.00	cop[tikv]	table:tt	range: decided by [eq(test.tt.c, Column#20) eq(test.tt.d, Column#21)], keep order:false, stats:pseudo

tests/integrationtest/t/planner/core/casetest/integration.test

@@ -716,4 +716,8 @@ select
 from
   (select 1 as c0) as subq_1;
 
-
+# TestIssue50614
+use test;
+drop table if exists tt;
+create table tt(a bigint, b bigint, c bigint, d bigint, e bigint, primary key(c,d));
+explain format = brief update tt, (select 1 as c1 ,2 as c2 ,3 as c3, 4 as c4 union all select 2,3,4,5 union all select 3,4,5,6) tmp set tt.a=tmp.c1, tt.b=tmp.c2 where tt.c=tmp.c3 and tt.d=tmp.c4 and (tt.c,tt.d) in ((11,111),(22,222),(33,333),(44,444));