Select `BB`.* ,`CC`.`ref cpt 2` from
(SELECT DISTINCT `Feuil1$`.Montant, `AA`.`ref cpt 1`
FROM `C:\temp\Classeurpol-2.xlsx`.`Feuil1$` `Feuil1$`
left outer join (select `Feuil1$`.Montant, `Feuil1$`.`ref cpt 1` from `C:\temp\Classeurpol-2.xlsx`.`Feuil1$` `Feuil1$` where `Feuil1$`.`ref cpt 1` is not null) `AA` on `Feuil1$`.Montant = `AA`.Montant) `BB`
left outer join (select `Feuil1$`.Montant, `Feuil1$`.`ref cpt 2` from `C:\temp\Classeurpol-2.xlsx`.`Feuil1$` `Feuil1$` where `Feuil1$`.`ref cpt 2` is not null) `CC` on `BB`.Montant = `CC`.Montant