This is an automated cherry-pick of pingcap#51329

Signed-off-by: ti-chi-bot <[email protected]>

Author: time-and-fate

planner/core/logical_plans.go

@@ -1140,9 +1140,13 @@ 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
 }
 

planner/core/rule_predicate_push_down.go

@@ -505,11 +505,15 @@ func (p *LogicalProjection) PredicatePushDown(predicates []expression.Expression
 			return predicates, child
 		}
 	}
+<<<<<<< HEAD:planner/core/rule_predicate_push_down.go
 	if len(p.children) == 1 {
 		if _, isDual := p.children[0].(*LogicalTableDual); isDual {
 			return predicates, p
 		}
 	}
+=======
+	exprCtx := p.SCtx().GetExprCtx()
+>>>>>>> 27ce02afd2e (planner: remove the limitation that predicates can't be pushed through `Projection` on `TableDual` (#51329)):pkg/planner/core/rule_predicate_push_down.go
 	for _, cond := range predicates {
 		substituted, hasFailed, newFilter := expression.ColumnSubstituteImpl(cond, p.Schema(), p.Exprs, true)
 		if substituted && !hasFailed && !expression.HasGetSetVarFunc(newFilter) {