planner: make sure mpp join task's hashCols are all contained of its …

…plan's schema (#52836) (#55654)

close #42587

pkg/planner/core/rule_eliminate_projection.go

@@ -131,7 +131,11 @@ func doPhysicalProjectionElimination(p PhysicalPlan) PhysicalPlan {
  }
  child := p.Children()[0]
  if childProj, ok := child.(*PhysicalProjection); ok {
- childProj.SetSchema(p.Schema())
+ // when current projection is an empty projection(schema pruned by column pruner), no need to reset child's schema
+ // TODO: avoid producing empty projection in column pruner.
+ if p.Schema().Len() != 0 {
+ childProj.SetSchema(p.Schema())
+ }
  }
  for i, col := range p.Schema().Columns {
  if p.SCtx().GetSessionVars().StmtCtx.ColRefFromUpdatePlan.Has(int(col.UniqueID)) && !child.Schema().Columns[i].Equal(nil, col) {