code: func conds2TableDual(p LogicalPlan, conds []expression.Expression) LogicalPlan {
  	if len(conds) != 1 {
  		return nil
  	}
  	con, ok := conds[0].(*expression.Constant)
  	if !ok {
  		return nil
  	}
  	sc := p.context().GetSessionVars().StmtCtx
  	if isTrue, err := con.Value.ToBool(sc); (err == nil && isTrue == 0) || con.Value.IsNull() {
  		dual := LogicalTableDual{}.Init(p.context())
  		dual.SetSchema(p.Schema())
  		return dual
  	}
  	return nil
  }
docs: // conds2TableDual builds a LogicalTableDual if cond is constant false or null.